This research was supported by a Hermes Fellowship to Ola Negm and Tanya Monaghan and through separate funding from the Nottingham Digestive Diseases Centre and the NIHR Nottingham Digestive Diseases Biomedical Research Centre.

1. Preparing a Microarray Plate
<ol>
	<li>Dilute C. difficile antigens with a printing buffer [PBS-Tween-trehalose (50 mM)] at the optimum concentration (which was predefined before running the patient sera): toxin A (200 &#181;g/mL) and toxin B (100 &#181;g/mL), pCDTb (200 &#181;g/mL), and purified native whole SLPs derived from ribotypes 001, 002, and 027 (200 &#181;g/mL). 
	NOTE: Toxin B was obtained from a toxin B-expressing strain CCUG 20309 (90 &#181;g/mL).
	<ol>
		<li>Dilute the positive controls, ...

<ol>
	<li>Negm, O. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Profiling+humoral+immune+responses+to+Clostridium+difficile.-specific+antigens+by+protein+microarray+analysis.">Profiling humoral immune responses to Clostridium difficile.-specific antigens by protein microarray analysis.</a> Clinical and Vaccine Immunology. 22 (9), 1033-1039 (2015).</li><li>Monaghan, T. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+prevalence+of+subclass-specific+binding+and+neutralizing+antibodies+against+Clostridium+difficile.+toxins+in+adult+cystic+fibrosis+sera:+possible+mode+of+immunoprotection+against+symptomatic+C.+difficile+infection.">High prevalence of subclass-specific binding and neutralizing antibodies against Clostridium difficile. toxins in adult cystic fibrosis sera: possible mode of immunoprotection against symptomatic C. difficile infection.</a> Clinical and Experimental Gastroenterology. 10, 169-175 (2017).</li><li>Negm, O. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protective+antibodies+against+Clostridium+difficile.+are+present+in+intravenous+immunoglobulin+and+are+retained+in+humans+following+its+administration.">Protective antibodies against Clostridium difficile. are present in intravenous immunoglobulin and are retained in humans following its administration.</a> Clinical &amp; Experimental Immunology. 188 (3), 437-443 (2017).</li><li>Monaghan, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=OC-058+A+protein+microarray+assay+for+predicting+severe+outcomes+in+Clostridium+difficile+infection.">OC-058 A protein microarray assay for predicting severe outcomes in Clostridium difficile infection.</a> Gut. 66, 31 (2017).</li><li>Bacon, A. 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In this protocol, we have shown that microarray is a suitable platform for defining humoral immune responses to C. difficile protein antigens in patient sera (Figures 3 and 6) and commercial preparations of IVIg (Figure 5). We have also demonstrated that the microarray technique performs well when compared to conventional ELISA (Figure 2) and shows excellent reproducibility, with intra- and inter-assay variabilities fal...

This protocol describes the development and validation of a novel and customized protein microarray assay for the detection and semi-quantification of bacterial strain and isotype-specific antibody responses to C. difficile antigens. We successfully use our C. difficile-specific microarray assay as a promising new tool for the compositional bioanalysis of specific antibody content in patient sera1,2, preparations of IVIg3, and identification of antibody specificities that correlate with poor outcomes in CDI4. We demonstrate how biobanked serum samples and commercial preparations of IVIg can be analyzed on microarray slides, allowing high-quality reproducible profiling of C. difficile pathogen-specific antibody responses in this assay.
Many healthy children and adults have detectable serum IgG and IgA antibodies to C. difficile toxins A and B5,6. These are thought to arise following transient exposure during infancy and following exposure to C. difficile in adulthood. For this reason, polyclonal IVIg has been used off-label to treat both recurrent and fulminant CDI7,8,9. However, its definitive role and mode of action remains unclear. Several studies have shown that the humoral immune response to C. difficile toxins plays a role in disease presentation and outcome. Specifically, asymptomatic patients show an increased serum anti-toxin A IgG concentration compared to patients who develop symptomatic disease10. A demonstrable association has been reported for median anti-toxin A IgG titers and 30-day all-cause mortality11. Several reports have also revealed an association with a protection against recurrence and antibody responses to toxin A, B, and several non-toxin antigens (Cwp66, Cwp84, FliC, FliD, and surface layer proteins (SLPs))12,13,14,15. These observations have spurred the development of the first passive immunotherapy drug targeting C. difficile toxin B (bezlotuxumab), which has recently been approved by the US Food and Drug Administration and the European Medicines Agency for the prevention of recurrent CDI16. Vaccination strategies using inactivated toxins or recombinant toxin fragments are also currently under development17,18,19. These new therapeutic approaches will undoubtedly stimulate the requirement for evaluating humoral immune responses to multiple antigens in large sample sizes.
Today, there is a notable lack of commercially available high-throughput assays capable of simultaneously assessing bacterial strain and isotype-specific antibody responses to C. difficile antigens. There is an unmet need to develop such assays to facilitate future research efforts and clinical applications. Protein microarrays are a method to immobilize large numbers of individually-purified proteins as a spatially organized array of spots onto a microscopic slide-based surface by using a robotic system, which can be either a contact20 or a non-contact printing tool21. The spots may represent complex mixtures such as cell lysates, antibodies, tissue homogenates, endogenous or recombinant proteins or peptides, body fluids or drugs22,23.
Protein microarray technology offers distinct advantages over standard in-house ELISA techniques, which have traditionally been used to assess anti-C. difficile antibody responses. These include an increased capacity for detecting a range of multi-isotype-specific antibodies against a more extensive panel of protein targets, reduced volume requirements for antigens, samples, and reagents, and an enhanced ability to incorporate a larger number of technical replicates, in addition to multiple internal quality control (QC) measures1. Microarrays are therefore more sensitive, accurate, and reproducible and have a greater dynamic range. These factors make microarrays a cheaper and potentially favorable alternative to ELISAs for the large-scale detection of known proteins. However, disadvantages of microarray technology result mainly from the large up-front costs associated with establishing a panel of highly purified antigens and setting up the technological platform.
Protein microarrays have been extensively used over the past two decades as a diagnostic and basic research tool in clinical applications. Specific applications include protein expression profiling, the study of enzyme-substrate relationships, biomarker screening, analysis of host-microbe interactions, and profiling antibody specificity23,24,25,26,27,28. Many new pathogen protein/antigen microarrays have been established, including malaria (Plasmodium)29, HIV-130, influenza31, severe acute respiratory syndrome (SARS)32, viral hemorrhagic fever33, herpesviruses34, and tuberculosis35.
The present protocol relates to the establishment of an easy operating C. difficile reactive antigen microarray assay, which enables accurate, precise, and specific quantification of multi-isotype and strain-specific antibody responses to C. difficile antigens in sera and polyclonal IVIg. Herein, we include representative results pertaining to an acceptable microarray assay performance when compared to ELISA as well as assay precision and reproducibility profiles. This assay could be further developed to profile other clinical samples and sets a new standard for research into the molecular basis of CDI.

<table border="0" cellpadding="0" cellspacing="0" style="width:1827px;" width="1826">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">BioRobotics MicroGrid II arrayer</td>
			<td style="width:296px;">Digilab, Malborough, MA, USA</td>
			<td style="width:296px;">N/A</td>
			<td style="width:836px;">Contact arrayer used to automated spotting of the antigens onto the slides.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Scanner InnoScan 710.</td>
			<td>Innopsys</td>
			<td>N/A</td>
			<td>A fluorescent microarray slide scanner with a red (Cy5) laser to read the reaction.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MAPIX software version 7.2.0</td>
			<td>Innopsys</td>
			<td>N/A</td>
			<td>Measure signal intensities of the spots.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Silicon contact pin</td>
			<td>Parallel Synthesis Technologies</td>
			<td>SMT-P75</td>
			<td>Print the samples onto the slides.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Thermo Scientific Nalgene Desiccator</td>
			<td>Thermo Scientific</td>
			<td>41102426</td>
			<td>To store the new and printed slides.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">384-well plate</td>
			<td>Genetix</td>
			<td>X7022UN</td>
			<td>To prepare the antigens.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Plate cover</td>
			<td>Sigma Aldrich, UK</td>
			<td>CLS6570-100EA</td>
			<td>To reduce evaporation of the samples.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Aminosilane slides</td>
			<td>Schott,&#160; Germany</td>
			<td>1064875</td>
			<td>The slide of choice for printing the antigens.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Slide holders</td>
			<td>GraceBio Labs, USA</td>
			<td>204862</td>
			<td>Divide the slides into identical 16 subarrays. These holders are re-usable, removable, leak-proof wells .&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Candida albicans lysate</td>
			<td>NIBSC</td>
			<td>PR-BA117-S</td>
			<td>Positive control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tetanus Toxoid&#160;</td>
			<td>Athens Research and Technology</td>
			<td>04/150</td>
			<td>Positive control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunoglobulin G (IgG), Normal Human Plasma</td>
			<td>&#160;Athens research and&#160; technology&#160;&#160;</td>
			<td>16-16-090707</td>
			<td>Purified Native Human Immunoglobulin G IgG, Human Plasma.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunoglobulin G1 (IgG1), Normal Human Plasma</td>
			<td>&#160;Athens research and&#160; technology&#160;&#160;</td>
			<td>16-16-090707-1</td>
			<td>Purified Native Human Immunoglobulin G1 IgG1, Human Plasma.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunoglobulin G2 (IgG2), Normal Human Plasma</td>
			<td>&#160;Athens research and&#160; technology&#160;&#160;</td>
			<td>16-16-090707-2</td>
			<td>Purified Native Human Immunoglobulin G2 IgG2, Human Plasma.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunoglobulin G3 (IgG3), Normal Human Plasma</td>
			<td>&#160;Athens research and&#160; technology&#160;&#160;</td>
			<td>16-16-090707-3</td>
			<td>Purified Native Human Immunoglobulin G3 IgG3, Human Plasma.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunoglobulin G4 (IgG4), Normal Human Plasma</td>
			<td>&#160;Athens research and&#160; technology&#160;&#160;</td>
			<td>16-16-090707-4</td>
			<td>Purified Native Human Immunoglobulin G4 IgG4, Human Plasma.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunoglobulin A (IgA), Human Plasma</td>
			<td>&#160;Athens research and&#160; technology&#160;&#160;</td>
			<td>16-16-090701</td>
			<td>Purified Native Human Immunoglobulin A (IgA), Human Plasma.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunoglobulin A1 (IgA1), Human Myeloma Plasma</td>
			<td>&#160;Athens research and&#160; technology&#160;&#160;</td>
			<td>16-16-090701-1M</td>
			<td>Purified Native Human Immunoglobulin A1 (IgA1), Human Plasma.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunoglobulin A2 (IgA2), Human Myeloma Plasma</td>
			<td>&#160;Athens research and&#160; technology&#160;&#160;</td>
			<td>16-16-090701-2M</td>
			<td>Purified Native Human Immunoglobulin A2 (IgA2), Human Plasma.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunoglobulin M (IgM), Human Plasma</td>
			<td>&#160;Athens research and&#160; technology&#160;&#160;</td>
			<td>16-16-090713</td>
			<td>Purified Native Human Immunoglobulin M (IgM), Human Plasma.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Biotinylated Goat Anti-Human IgG Antibody, gamma chain specific</td>
			<td>Vector Labs</td>
			<td>BA-3080</td>
			<td>Goat anti- human IgG (&#947;-chain specific)-biotin antibody reacts specifically with human IgG but not with other immunoglobulins.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mouse Anti-Human IgG1 Hinge-BIOT</td>
			<td>Southern Biotec</td>
			<td>9052-08&#160;</td>
			<td>Goat anti- human IgG1 biotin antibody reacts specifically with human IgG1 but not with other immunoglobulins.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mouse Anti-Human IgG2 Fc-BIOT</td>
			<td>Southern Biotec</td>
			<td>9060-08&#160;&#160;</td>
			<td>Goat anti- human IgG2 -biotin antibody reacts specifically with human IgG 2but not with other immunoglobulins.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mouse Anti-Human IgG3 Hinge-BIOT</td>
			<td>Southern Biotec</td>
			<td>9210-08&#160;&#160;&#160;</td>
			<td>Goat anti- human IgG3-biotin antibody reacts specifically with human IgG3 but not with other immunoglobulins.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mouse Anti-Human IgG4 pFc&#39;-BIOT</td>
			<td>Southern Biotec</td>
			<td>9190-08&#160;&#160;</td>
			<td>Goat anti- human IgG-biotin antibody reacts specifically with human IgG but not with other immunoglobulins.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Anti-Human IgA, alpha chain specific, made in goat - Biotinylated</td>
			<td>Vector Labs</td>
			<td>BA-3030</td>
			<td>Goat anti- human IgG -biotin antibody reacts specifically with human IgG but not with other immunoglobulins.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mouse Anti-Human IgA1-BIOT</td>
			<td>Southern Biotec</td>
			<td>9130-08</td>
			<td>Goat anti- human IgG -biotin antibody reacts specifically with human IgG but not with other immunoglobulins.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mouse Anti-Human IgA2-BIOT</td>
			<td>Southern Biotec</td>
			<td>9140-08&#160;&#160;</td>
			<td>Goat anti- human IgG -biotin antibody reacts specifically with human IgG but not with other immunoglobulins.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mouse Anti-Human IgM-BIOT</td>
			<td>Southern Biotec</td>
			<td>9020-08&#160;</td>
			<td>Goat anti- human IgG-biotin antibody reacts specifically with human IgG but not with other immunoglobulins.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">0.2 mm syringe filter</td>
			<td>Thermo scientific</td>
			<td>723-2520</td>
			<td>Filter the 5% BSA.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bovine Serum Albumin (BSA)</td>
			<td>Sigma Aldrich, UK</td>
			<td>A7284</td>
			<td>Use 5% BSA for blocking the slides.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Antibody diluent</td>
			<td>Dako, UK</td>
			<td>S3022</td>
			<td>To dilute the serum and the secondary antibody.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Streptavidin Cy5</td>
			<td>eBioscience</td>
			<td>SA1011</td>
			<td>Detection of the immune reaction.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Purified whole C. difficile toxins A and B (toxinotype 0, strain VPI 10463, ribotype 087)</td>
			<td>Toxins Group, Public Health England</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Purified whole C. difficile toxin B (CCUG 20309 toxin B only expressing strain)</td>
			<td>Toxins Group, Public Health England</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Precursor form of B fragment of binary toxin, pCDTb</td>
			<td>University of Bath&#160;</td>
			<td>NA</td>
			<td>Produced in E. Coli from wholly synthetic recombinant gene construct. Amino acid sequence based on published sequence from 027 ribotype (http:www.uniprot.org/uniprot/A8DS70)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Purified native whole ribotype-specific (001, 002, 027) surface layer proteins</td>
			<td>Dublin City University&#160;</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Vigam (IVIg preparation 1)</td>
			<td>Nottingham University Hospitals NHS Trust</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Privigen (IVIg preparation 2)</td>
			<td>Nottingham University Hospitals NHS Trust</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Intratect (IVIg preparation 3)</td>
			<td>Nottingham University Hospitals NHS Trust</td>
			<td>N/A</td>
			<td></td>
		</tr>
	</tbody>
</table>

a protein microarray assay for serological determination of antigen-specific antibody responses following clostridium difficile infection

We provide a detailed overview of a novel high-throughput protein microarray assay for the determination of anti-Clostridium difficile antibody levels in human sera and in separate preparations of polyclonal intravenous immunoglobulin (IVIg). The protocol describes the methodological steps involved in sample preparation, printing of arrays, assay procedure, and data analysis. In addition, this protocol could be further developed to incorporate diverse clinical samples including plasma and cell culture supernatants. We show how protein microarray can be used to determine a combination of isotype (IgG, IgA, IgM), subclass (IgG1, IgG2, IgG3, IgG4, IgA1, IgA2), and strain-specific antibodies to highly purified whole C. difficile toxins A and B (toxinotype 0, strain VPI 10463, ribotype 087), toxin B from a C. difficile toxin-B-only expressing strain (CCUG 20309), a precursor form of a B fragment of binary toxin, pCDTb, ribotype-specific whole surface layer proteins (SLPs; 001, 002, 027), and control proteins (tetanus toxoid and Candida albicans). During the experiment, microarrays are probed with sera from individuals with C. difficile infection (CDI), individuals with cystic fibrosis (CF) without diarrhea, healthy controls (HC), and from individuals pre- and post-IVIg therapy for the treatment of CDI, combined immunodeficiency disorder, and chronic inflammatory demyelinating polyradiculopathy. We encounter significant differences in toxin neutralization efficacies and multi-isotype specific antibody levels between patient groups, commercial preparations of IVIg, and sera before and following IVIg administration. Also, there is a significant correlation between microarray and enzyme-linked immunosorbent assay (ELISA) for antitoxin IgG levels in serum samples. These results suggest that microarray could become a promising tool for profiling antibody responses to C.difficile antigens in vaccinated or infected humans. With further refinement of antigen panels and a reduction in production costs, we anticipate that microarray technology may help optimize and select the most clinically useful immunotherapies for C. difficile infection in a patient-specific manner.

Figure 1 illustrates a flowchart describing the major steps in the described protocol. Figure 2 shows Spearman correlation tests demonstrating significant agreement between microarray and ELISA for IgG and IgA anti-toxin A and B levels in the patient test sera. Figure 3 shows differential IgG and IgA antibody-class specific antibody responses to toxin A, toxin B, and binary toxin (pCDTb) in patients ...

Watch this Scientific Journal Video about A Protein Microarray Assay for Serological Determination of Antigen-specific Antibody Responses Following Clostridium difficile Infection at JoVE.com

A Protein Microarray Assay for Serological Determination of Antigen-specific Antibody Responses Following Clostridium difficile Infection

This article describes a simple protein microarray method for profiling humoral immune responses to a 7-plex panel of highly purified Clostridium difficile antigens in human sera. The protocol can be extended for the determination of specific antibody responses in preparations of polyclonal intravenous immunoglobulin.

A Protein Microarray Assay for Serological Determination of Antigen-specific Antibody Responses Following Clostridium difficile Infection

We provide a detailed overview of a novel high-throughput protein microarray assay for the determination of anti-Clostridium difficile antibody levels in ...

This method may help with optimizing and selecting clinically useful immunotherapies for Clostridium difficile infection in a patient-specific manner, and elucidating human immune responses to Clostridium difficile. The main advantage of this technique is that it enables accurate and simultaneous quantification of multi isotype and strain-specific antibody responses to C.difficile antigens. Generally, individuals that are new to this method will struggle because expertise is required in establishing and optimizing a panel of highly purified antigens, and setting up the technological platform.Visual demonstration of this method is critical, as methodological list types involved in preparing the microwave plate, arrays printing, a safe procedure, and the data analysis require attention to the details. Demonstrating some of the procedure will be by Sam Greenwood, a technician from my laboratory. To begin, dilute Clostridium difficile antigens and printing buffer to optimum concentration.Next, transfer 10 microliters of antigen solution to a 384 well plate. Cover the plate with a plate seal, and centrifuge at 300 times gravity for five minutes at room temperature. For microarray printing, use a hand-held gas burner to heat the silicon PIN three times for two seconds each.Then, rinse the silicon PIN in clean water three times for three seconds each. Place the microarray plate in the loading cartridge of an arrayer. Eject the tray, and then place the amino silane slides in the slide tray and press the OK button to turn the vacuum on.Insure that all of the slides are secured, and then click OK.Return the tray to the origin, and close the lid. Next, launch the appropriate program and go to File, then Microarraying Parameters, then Open. Select Clostridium difficile file for printing all antigens in quadruplicate.Under this window, open the Source tab to indicate sample storage, and Target tab to input microarray details. Then, open the Options tab to select the washing tool. Under the General tab of Run Preferences, on the TAS applications suite toolbar, select Wash at start of run, and Wash at end of run.Open the Climate tab, and set the humidity level between 55 to 60%Now start the run, and periodically check the arrayer to insure proper functioning. After printing, carefully place the printed slides in a slide holder with 16 multi-well chambers. Then add 100 microliters of 5%BSAT to each block.Cover the slides and incubate for one hour at room temperature with shaking. Use 120 microliters of PBST to wash each block five times for one minute each with shaking. Next, thaw out the serum samples obtained from C difficile infected patients and healthy controls on ice for 20 minutes.Add commercially available antibody diluent to the master block, and then add samples to the master block and mix. Discard the washing buffer and add 100 microliters of each diluted sample to the experimental blocks. For the negative control block, add 100 microliters of only the antibody diluent.Then, incubate the slides for one hour at room temperature with gentle shaking. Next, use 120 microliters of PBST to wash each block five times for three minutes each with shaking. Then add 100 microliters of biotinylated goat anti-Human antibody diluted in antibody diluent to each block.Cover the slides and incubate for one hour at room temperature with gentle shaking. Use 120 microliters of PBST to wash each block five times for three minutes each with shaking. Next, add 100 microliters of streptavidin SY5 conjugate diluted in 5%BSAT, in a ratio of one to two thousand to each block.Cover the slides with foil and incubate for 15 minutes at room temperature with gentle shaking. Wash the slides first with 120 microliters of PBST five times for one minute each, and then wash them two more times for one minute each with PBS. To dry the slides, spin them for five minutes at 300 times gravity.Turn the laser scanner on 30 minutes prior to scanning, to allow it to warm up. Then place the slide in the scanner with the printed surface facing up until the plate light turns solid green. Next, press the Settings button.On the first tab, insure that the Automatic scrolling and Barcode are unchecked. Then, set the Pixel size to 10, Scan Mode to Medium, Acquisition to 635 only, Acquisition Mode to Manual, gain to 20, and power to low. On the second tab, insure that the slide type is unlabeled.On the third tab, set the Focus setting to Auto focus. Press the import grid button to select the appropriate array list associated with the scanned image. Then, press the autofind button to align the grid to the spots on the slide.Finally, press the Quantification Process button to measure the fluorescence intensity of each spot. Then, save the results in an appropriate format for further analysis. In this protocol, a protein microarray is compared with ELISA to assess the reproducibility between these two techniques.The Spearman correlation coefficient analysis shows significant agreement between the microarray and ELISA for detecting IgG Anti-toxin A, and Anti-toxin B levels in serum samples. Intro assay and inter assay reproducibility of the protein micro array are calculated using the serum samples of seven patients. The samples analyzed on two different array slides against Toxin A, Toxin B, SLP001, SLP002, SLP027, Toxin B from Toxin B only producing strain CCUG, and pCDTb antigens reveal good reproducibility.A protein microarray is performed to detect an isotype-specific antibody response against Clostridium difficile toxins. The serum samples of patients and healthy individuals are used to detect the levels of IgG and IgA against Toxin A, Toxin B, Toxin B from a Clostridium difficile Toxin B only expressing strain, and precursor form of a B fragment of binary toxin. Once mastered, this technique can be done in seven hours.The quality control experiment, different parameters such as selection of appropriate surface chemistry, printing buffers, blocking buffers, and dilutions of serum samples and secondary antibodies should be evaluated before running samples. Printing a high-quality array requires a good understanding of the array or software to adjust the printing of parameters according to the experimental protocol. It is crucial to maintain optimum performance of the arrayer, and a dust-free environment throughout the experiment.This technique will pave the way for researchers in the field of immunology and molecular biology, in terms of characterizing humoral immune responses to infection, and discovering serodiagnostic antigens. Don't forget that working with infected blood samples and bacterial toxins can be hazardous. In general, in laboratory, safety and standard precautions should always be taken into consideration while performing this procedure.

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Research

JoVE Journal

Immunology and Infection

10.0K vistas.  University of Nottingham. This method may help with optimizing and selecting clinically useful immunotherapies for Clostridium difficile infection in a patient-specific manner, and elucidating human immune responses to Clostridium difficile. The main advantage of this technique is that it enables accurate and simultaneous quantification of multi isotype and strain-specific antibody responses to C.difficile antigens. Generally, individuals that are new to this method will struggle because expertise is required in estab...