We thank all the members of the URCACyt, flow cytometry technical platform, the staff of the Department of Immunology, and the staff of the Department of Internal Medicine and Geriatrics, who contributed to optimizing and validating the protocol. This work was funded by Reims University Hospitals (grant number AOL11UF9156).

The protocol for human blood collection and handling was reviewed and approved by the regional ethics committee (CPP Est II), and the protocol number is 2011-A00594-37. Because the following protocol describes the handling of human blood, institutional guidelines for disposing of biohazardous material should be followed. Laboratory safety equipment, such as lab coats and gloves, should be worn.
1. Erythrocyte washing
NOTE: The day before handling, prepare a PBS-BSA bu...

Several techniques are available to determine the density of erythrocyte CR1 (CR1/E). The first techniques used were the agglutination of red blood cells by anti-CR1 antibodies31 and the formation of rosettes in the presence of erythrocytes coated with C3b32. These rudimentary techniques were rapidly replaced by immunostaining methods using radiolabeled anti-CR1 antibodies1,33. It is also possible to measure the con...

CR1 (complement receptor type 1, CD35) is a 200 kDa transmembrane glycoprotein present on the surface of many cell types, such as erythrocytes1, B lymphocytes2, monocytic cells, some T cells, follicular dendritic cells3, fetal astrocytes4, and glomerular podocytes5. CR1 interfering with its ligands C3b, C4b, C3bi6,7,8,9, a subunit of the first complement component, C1q10 and MBL (mannan-binding lectin)11 inhibits the activation of complement and is involved in humoral and cellular immune response.
In primates, including humans, erythrocyte CR1 is involved in the transport of immune complexes to the liver and spleen, to purify the blood and prevent their accumulation in vulnerable tissues such as the skin or kidneys12,13,14. This phenomenon of immune adhesion between immune complexes and erythrocytes depends on the number of CR1 molecules15. In humans, the mean density of CR1/E is only 500 (i.e., 500 molecules of CR1 per erythrocyte). This density varies from one individual to another (100&#8211;1,200 CR1/E) and from one erythrocyte to another in the same individual. Some individuals of &#34;null&#34; phenotype express fewer than 20 CR1/E16.
The density of CR1/E is regulated by two co-dominant autosomal alleles linked to a point mutation in intron 27 of the gene coding for CR1*117,18. This mutation produces an additional restriction site for the HindIII enzyme. The restriction fragments obtained after digestion with HindIII in this case are 7.4 kb for the allele linked to a strong expression of CR1 (H: high allele) and 6.9 kb for the allele linked to low CR1 expression (L: low allele). This link is found in Caucasians and Asians but not in people of African descent19.
The level of expression of erythrocyte CR1 is also correlated with the presence of point nucleotide mutations in exon 13 encoding SCR 10 (I643T) and in exon 19 encoding SCR16 (Q981H). It is high in homozygous 643I/981Q and low in homozygous 643T/981H individuals20. Thus, &#34;low&#34; individuals express around 150 CR1/E, &#34;medium&#34; individuals express around 500 CR1/E, and &#34;high&#34; individuals express around 1,000 CR1/E.
In addition to this erythrocyte density polymorphism, CR1 is characterized by a length polymorphism corresponding to four allotypes of different sizes: CR1*1 (190 kDa), CR1*2 (220 kDa), CR1*3 (160 kDa), and CR1*4 (250 kDa)21 and an antigenic polymorphism corresponding to the blood group KN22.
We present our method based on flow cytometry to determine the density of CR1/E. Using three subjects whose CR1/E density is known, expressing a low density level (180 CR1/E), a medium density level (646 CR1/E), and a high density level (966 CR1/E), it is easy to measure the mean fluorescence intensity (MFI) of their erythrocytes or red blood cells (RBC), or RBC MFI, after anti-CR1 immunostaining using a flow cytometer. One can then plot a standard line representing the MFI as a function of CR1/E density. Measuring the MFI of subjects whose CR1/E density is not known and comparing it to this standard line, it is possible to determine the individuals&#39; CR1/E density. This technique has been used for many years in the laboratory, and has enabled us to detect a reduction in the expression of erythrocyte CR1 in many pathologies such as systemic lupus erythematosus (SLE)23, Acquired immunodeficiency syndrome (AIDS)24, malaria25, and recently Alzheimer&#39;s disease (AD)26,27. The development of drugs targeting CR1 to couple with erythrocytes, as in the case of anti-thrombotic drugs28 requires the evaluation of CR1/E density, and the availability of a robust technique to quantify CR1.
The protocol presented runs in singlicate. It is adaptable to determine the density of CR1/E on many individuals using specific commercially available 96 well plates (see Table of Materials). To this end, it is easy to adapt our method to any 96 well plate. For each sample, a cell suspension of erythrocytes (0.5 x 106&#8211;1 x 106 erythrocytes) is distributed per well. For each well, first the primary anti-CR1 antibody is added, then streptavidin PE, the secondary anti-streptavidin antibody, and again streptavidin PE, using the same dilutions as those of our method, but by adapting volumes and respecting proportionality.
The blood samples from subjects of the range and from subjects to be quantified for CR1 should be drawn at the same time, stored in the refrigerator at 4 &#176;C, and handled at 4 &#176;C (on ice and/or in the refrigerator).

<table border="0" cellpadding="0" cellspacing="0" style="width:752px;" width="753">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">1000E Barrier Tip</td>
			<td style="width:239px;">Thermo Fischer Scientific , F-67403 Illkirch, France</td>
			<td style="width:119px;">2079E</td>
			<td style="width:179px;">sample pipetting</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">1-100 &#181;L Bevelled, filter tip</td>
			<td style="width:239px;">Starlab GmbH, D-22926 Ahrenburg, Germany</td>
			<td style="width:119px;">S1120-1840</td>
			<td>sample pipetting</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Biotinylated anti-CR1 monoclonal antibody (J3D3)</td>
			<td style="width:239px;">Home production of non-commercial monoclonal antibody, courtesy of Dr J. Cook</td>
			<td style="width:119px;"></td>
			<td>immunostaining</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Blouse</td>
			<td style="width:239px;"></td>
			<td style="width:119px;"></td>
			<td>protection</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Bovin serum albumin (7,5%)</td>
			<td style="width:239px;">Thermo Fischer Scientific , F-67403 Illkirch, France</td>
			<td style="width:119px;">15260037</td>
			<td>cytometry</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Centrifuge</td>
			<td style="width:239px;">Thermo Fischer Scientific , F-67403 Illkirch, France</td>
			<td style="width:119px;">11176917</td>
			<td>centrifugation</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Clean Solution</td>
			<td style="width:239px;">BD, F-38801 Le Pont de Claix, France</td>
			<td style="width:119px;">340345</td>
			<td>cytometry</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Comorack-96</td>
			<td style="width:239px;">Dominique DUTSCHER SAS, F-67172 Brumath</td>
			<td style="width:119px;">944060P</td>
			<td>rack</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Cytometer Setup &#38; Tracking Beads Kit</td>
			<td style="width:239px;">BD, F-38801 Le Pont de Claix, France</td>
			<td style="width:119px;">655051</td>
			<td>cytometry</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Formaldehyde solution 36.5 %</td>
			<td style="width:239px;">Sigma Aldrich, F-38070 Saint Quentin Fallavier, France</td>
			<td style="width:119px;">F8775-25ML</td>
			<td>Fixation</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">10 &#181;L Graduated, filter tip</td>
			<td style="width:239px;">Starlab GmbH, D-22926 Ahrenburg, Germany</td>
			<td style="width:119px;">S1121-3810</td>
			<td>sample pipetting</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">LSRFORTESSA Flow Cytometer</td>
			<td style="width:239px;">BD, F-38801 Le Pont de Claix, France</td>
			<td style="width:119px;">647788</td>
			<td>cytometry</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Microman Capillary Pistons</td>
			<td style="width:239px;">Dominique DUTSCHER SAS, F-67172 Brumath</td>
			<td style="width:119px;">067494</td>
			<td>sample pipetting</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Micronic 1.40 mL round bottom tubes</td>
			<td style="width:239px;">Dominique DUTSCHER SAS, F-67172 Brumath</td>
			<td style="width:119px;">MP32051</td>
			<td>mix</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Micropipette Microman - type M25 -</td>
			<td style="width:239px;">Dominique DUTSCHER SAS, F-67172 Brumath</td>
			<td style="width:119px;">066379</td>
			<td>sample pipetting</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Phosphate buffered Saline (PBS)</td>
			<td style="width:239px;">Thermo Fischer Scientific , F-67403 Illkirch, France</td>
			<td style="width:119px;">10010031</td>
			<td>cytometry</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Pipette PS 325 mm, 10 mL</td>
			<td style="width:239px;">Dominique DUTSCHER SAS, F-67172 Brumath</td>
			<td style="width:119px;">391952</td>
			<td>sample pipetting</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">powder-free Nitrile Exam gloves</td>
			<td style="width:239px;">Medline Industries, Inc, Mundelein, IL 60060, USA</td>
			<td style="width:119px;">486802</td>
			<td>sample protection</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Reference 2 pipette, 0,5-10 &#181;L</td>
			<td style="width:239px;">Eppendorf France SAS, F-78360 Montesson, France</td>
			<td style="width:119px;">4920000024</td>
			<td>sample pipetting</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Reference 2 pipette, 20-100 &#181;L</td>
			<td style="width:239px;">Eppendorf France SAS, F-78360 Montesson, France</td>
			<td style="width:119px;">4920000059</td>
			<td>sample pipetting</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">Reference 2 pipette, 100-1000 &#181;L</td>
			<td style="width:239px;">Eppendorf France SAS, F-78360 Montesson, France</td>
			<td style="width:119px;">4920000083</td>
			<td>sample pipetting</td>
		</tr>
		<tr height="55">
			<td height="55" style="height:55px;">Rinse Solution</td>
			<td style="width:239px;">BD, F-38801 Le Pont de Claix, France</td>
			<td style="width:119px;">340346</td>
			<td>cytometry</td>
		</tr>
		<tr height="55">
			<td height="55" style="height:55px;">Round bottom tube</td>
			<td style="width:239px;">Sarstedt, F-70150 Marnay, France</td>
			<td style="width:119px;">55.1579</td>
			<td>cytometry</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">Safe-Lock Tubes, 1.5 mL</td>
			<td style="width:239px;">Eppendorf France SAS, F-78360 Montesson, France</td>
			<td style="width:119px;">0030120086</td>
			<td>mix</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:216px;">streptavidin R-PE</td>
			<td style="width:239px;">Tebu Bio, F-78612 Le Perray-en-Yvelines, France</td>
			<td style="width:119px;">AS-60669</td>
			<td>immunostaining</td>
		</tr>
		<tr height="47">
			<td height="47" style="height:47px;width:216px;">Tapered Centrifuge Tubes 50 mL</td>
			<td style="width:239px;">Thermo Fischer Scientific , F-67403 Illkirch, France</td>
			<td>10203001</td>
			<td>mix</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Vector anti streptavidin biotin</td>
			<td style="width:239px;">Eurobio Ingen, F-91953 Les Ulis, France</td>
			<td style="width:119px;">BA-0500</td>
			<td>immunostaining</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Vortex-Genie 2</td>
			<td style="width:239px;">Scientific Industries, Inc, Bohemia, NY 111716, USA</td>
			<td style="width:119px;">SI-0236</td>
			<td>mix</td>
		</tr>
	</tbody>
</table>

measuring erythrocyte complement receptor 1 using flow cytometry

CR1 (CD35, Complement Receptor type 1 for C3b/C4b) is a high molecular weight membrane glycoprotein of about 200 kDa that controls complement activation, transports immune complexes, and participates in humoral and cellular immune responses. CR1 is present on the surface of many cell types, including erythrocytes, and exhibits polymorphisms in length, structure (Knops, or KN, blood group), and density. The average density of CR1 per erythrocyte (CR1/E) is 500 molecules per erythrocyte. This density varies from one individual to another (100&#8211;1,200 CR1/E) and from one erythrocyte to another in the same individual. We present here a robust flow cytometry method to measure the density of CR1/E, including in subjects expressing a low density, with the help of an amplifying immunostaining system. This method has enabled us to show the lowering of CR1 erythrocyte expression in diseases such as Alzheimer&#39;s disease (AD), systemic lupus erythematosus (SLE), AIDS, or malaria.

The erythrocytes of three subjects whose density of CR1 is known (&#34;low&#34; subject [180 CR1/E], &#34;medium&#34; subject [646 CR1/E], and &#34;high&#34; subject [966 CR1/E]), and of two subjects whose CR1 density needed to be determined were immunostained by an anti-CR1 antibody coupled to an amplification system using the phycoerythrin fluorochrome. At the beginning, the CR1 density of the subjects from the low-high range was determined by the Scatchard method29 using radiolabeled antibodies...

Watch this Scientific Journal Video about Measuring Erythrocyte Complement Receptor 1 Using Flow Cytometry at JoVE.com

Measuring Erythrocyte Complement Receptor 1 Using Flow Cytometry

The aim of this method is to determine the CR1 density in the erythrocytes of any subject by comparing with three subjects whose erythrocyte CR1 density is known. The method uses flow cytometry after immunostaining of the subjects&#39; erythrocytes by an anti-CR1 monoclonal antibody coupled to an amplified system using phycoerythrin (PE).

CR1 (CD35, Complement Receptor type 1 for C3b/C4b) is a high molecular weight membrane glycoprotein of about 200 kDa that controls complement activation, ...

This protocol can be used to measure the number of antigenic sites on cellular receptor of interest. The main advantage of this technique is that it produces robust results, even for receptors expressed at a low density. This method enables the evaluation of the reduction of CR1 erythrocyte expression and this is such as Alzheimer's, systemic lupus erythematosus, AIDS, and malaria.This protocol is useful for any analysis of cell receptor density and can also be applied to the study of cell receptor expression by fluorescence microscope. We recommend spacing out the tubes during the cell and antibody distribution, and to be accompanied by a cytometric specialist during the first analysis if possible. Visual demonstration of the immunostaining and density quantification by flow cytometry is critical for understanding how to properly set the analysis parameters.Before beginning the analysis, add 250 microliters of sodium EDTA anticoagulated whole blood from blood storage tubes into a 50 milliliter conical tube containing 20 milliliters of four degree Celsius PBS-BSA. Mix the tube contents by gentle inversion and spin the cells by centrifugation. Use a 10 milliliter pipette to discard the supernatant and carefully resuspend the pellet in the residual volume of solution.Add 20 milliliters of cold PBS-BSA and centrifuge the cells again. At the end of the centrifugation, place the tube in a rack, placed on ice and transfer eight microliters of the washed erythrocytes into a 50 milliliter tube containing three milliliters of PBS-BSA. Then mix the erythrocytes gently by spinning to obtain a homogenous cell suspension.For erythrocyte immunostaining, carefully transfer 100 microliters of the diluted erythrocytes into individual 1.5 milliliter tubes and collect the red blood cells by centrifugation. After discarding the supernatants, carefully add 20 microliters of a 0.5 microgram per microliter concentration of biotinylated anti-CR1 J3D3 antibody in PBS-BSA, directly to each pellet. Add 20 microliters of PBS-BSA buffer alone to the negative control cells with gentle mixing and incubate the samples for 45 minutes at four degrees Celsius.At the end of the incubation, wash the samples two times with 750 microliters of fresh PBS-BSA per tube, per wash. After the second wash, add 20 microliters of a one to 10 dilution of streptavidin phycoerythrin in PBS-BSA to each tube with gentle mixing, and incubate the samples for 45 minutes at four degrees Celsius. At the end of the incubation, wash the samples twice, as demonstrated.After the second wash, fix each cell sample pellet with 450 microliters of fixation buffer during vortexing, before transferring each sample into individual five milliliter round bottom tubes for up to 48 hours of storage at four degrees Celsius. To analyze the immunostained erythrocytes for flow cytometry, click the new experiment button in the flow cytometer, and rename the new experiment. Select forward scatter, side scatter and PE in the cytometer settings window.In the open experiment, select cytometer settings application settings and create a global worksheet, using the gray boxes and cross hairs to guide the optimization. When all of the parameters have been set, load the unstained control tube onto the cytometer and run the acquisition, optimizing the forward and side scatter voltages to eliminate debris and to ensure that the population of interest is on scale. Next, draw a gate around the red blood cells on the forward versus side scatter plot and display the red blood cell population in the dot plot of PE fluorescence.If the positive populations are on scale, load the stained control tube onto the cytometer and run the acquisition. To record and analyze samples, unload the stained sample and create a forward versus side scatter plot and a PE fluorescence histogram on a new global worksheet. Load the first sample onto the cytometer, run the acquisition and draw a red blood cell gate around the erythrocytes in the forward versus side scatter plot.Display the red blood cell population in the PE fluorescence histogram and under the statistics tab, select the mean for the PE fluorescence parameters on red blood cell populations. In the acquisition dashboard, select all of the events in the stopping gate and 10, 000 events to record, and click record data. When the event recording has completed, remove the tube from the cytometer.The global worksheet plots should look as illustrated. Flow cytometric analysis of immunostained erythrocytes from three subjects of known CR1 densities allows measurement of the mean fluorescence intensity of the labeling for each subject. Plotting a curve using the values of the subject with the known density of erythrocyte CR1 allows these data to be reported as a function of the mean fluorescence intensity.Comparison of the regression line resulting from this curve to the values of the mean fluorescence intensity of the other subjects allows determination of their CR1 erythrocyte density. Take care that the erythrocytes and antibodies are properly distributed, so the calibration curves of the experimented samples on the negative control are within the range of the cytometer settings. It is possible to adapt this procedure to measure other density cellular receptors, simply by changing the primary antibody and/or adapting the amplification layers.Whenever you are handling blood, there is a risk of pathogen contamination. Therefore, be sure to use good laboratory practices and to wear the appropriate personal protective equipment.

Measuring Erythrocyte Complement Receptor 1 Using Flow Cytometry

Abstract