We are grateful to the whole blood donors and all the health personnel who took the blood samples.

The study was approved by the ethical committee of Pisa University, and informed and signed consent was obtained from each donor.
1. Formation of &#947;H2AX and 53BP1 foci
<ol>
	<li>Preparation of samples and mutagenic treatment
	<ol>
		<li>Collect whole blood samples by venipuncture from healthy adult individuals in blood collection (e.g., Vacutainer) tubes containing lithium heparin as an anticoagulant.</li>
		<li>In order to guarantee proper blood sample preserva...

<ol>
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C., Oliver, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Permeabilization+of+the+cell+membrane.">Permeabilization of the cell membrane.</a> Methods in Molecular Biology. 588, 63-66 (2010).</li><li>Hecht, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bleomycin:+New+perspectives+on+the+mechanism+of+action.">Bleomycin: New perspectives on the mechanism of action.</a> Journal of Natural Products. 63, 158-168 (2000).</li><li>Fei, P., El-Deiry, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=P53+and+radiation+responses.">P53 and radiation responses.</a> Oncogene. 22, 5774-5783 (2003).</li><li>Mahaney, B. L., Meek, K., Lees-Miller, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Repair+of+ionizing+radiation-induced+DNA+double-strand+breaks+by+non-homologous+end-joining.">Repair of ionizing radiation-induced DNA double-strand breaks by non-homologous end-joining.</a> Biochemical Journal. 417 (3), 639-650 (2009).</li><li>Palla, V., 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=Gamma-H2AX:+Can+it+be+established+as+a+classical+cancer+prognostic+factor.">Gamma-H2AX: Can it be established as a classical cancer prognostic factor.</a> Tumor Biology. 39 (3), 1010428317695931 (2017).</li><li>Markov&#224;, E., Hillert, L., Malmgren, L., Persson, B. R. R., Belyaev, I. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microwaves+from+GSM+mobile+telephones+affect+53BP1+and+gamma-H2AX+foci+in+human+lymphocytes+from+hypersensitive+and+healthy+persons.">Microwaves from GSM mobile telephones affect 53BP1 and gamma-H2AX foci in human lymphocytes from hypersensitive and healthy persons.</a> Environmental Health Perspectives. 113 (9), 1172-1177 (2005).</li><li>Scarpato, R., 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=Nuclear+damage+in+peripheral+lymphocytes+of+obese+and+overweight+Italian+children+as+evaluated+by+the+&#947;-H2AX+focus+assay+and+micronucleus+test.">Nuclear damage in peripheral lymphocytes of obese and overweight Italian children as evaluated by the &#947;-H2AX focus assay and micronucleus test.</a> The FASEB Journal. 25 (2), 685-693 (2018).</li><li>Shanbhag, N. 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=Early+neuronal+accumulation+of+DNA+double-strand+breaks+in+Alzheimer's+disease.">Early neuronal accumulation of DNA double-strand breaks in Alzheimer's disease.</a> Acta Neuropathologica Communication. 7 (1), 77 (2019).</li><li>Lassmann, 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=In+vivo+formation+of+gamma-H2AX+and+53BP1+DNA+repair+foci+in+blood+cells+after+radioiodine+therapy+of+differentiated+thyroid+cancer.">In vivo formation of gamma-H2AX and 53BP1 DNA repair foci in blood cells after radioiodine therapy of differentiated thyroid cancer.</a> Journal of Nuclear Medicine. 51 (8), 1318-1325 (2010).</li><li>Derlin, 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=Assessment+of+&#947;-H2AX+and+53BP1+foci+in+peripheral+blood+lymphocytes+to+predict+subclinical+hematotoxicity+and+response+in+somatostatin+receptor-targeted+radionuclide+therapy+for+advanced+gastroenteropancreatic+neuroendocrine+tumors.">Assessment of &#947;-H2AX and 53BP1 foci in peripheral blood lymphocytes to predict subclinical hematotoxicity and response in somatostatin receptor-targeted radionuclide therapy for advanced gastroenteropancreatic neuroendocrine tumors.</a> Cancers (Basel). 13 (7), 1516 (2021).</li><li>Djuzenova, C. S., 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=Radiosensitivity+in+breast+cancer+assessed+by+the+histone+&#947;-H2AX+and+53BP1+foci.">Radiosensitivity in breast cancer assessed by the histone &#947;-H2AX and 53BP1 foci.</a> Radiation Oncology. 24, 8-98 (2013).</li><li>Atkinson, J., Bezak, E., Kempson, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+DNA+double-strand+breaks+-+are+we+there+yet.">Imaging DNA double-strand breaks - are we there yet.</a> Nature Reviews in Molecular Cell Biology. 23, 579-580 (2022).</li></ol>

Immunofluorescence analysis of &#947;H2AX and 53BP1 foci is a suitable method for assessing genomic damage in interphase nuclei of a cell system. This procedure has several critical points that can affect the outcome of the experiments, mainly, the agents used in fixation and permeabilization, the type of antibodies and their dilution factors, and the concentration of the mutagen.
The maintenance of protein integrity is fundamental since the immunofluorescence method expects to identify antige...

DNA damage is continuously induced by agents that can be endogenous, such as ROS generated by cellular oxidative metabolism, or exogenous, both chemicals and physical1. Among the most harmful lesions, double-strand breaks (DSBs) play a fundamental role in contributing to genomic instability, since they cause chromosome aberrations that in turn can initiate the carcinogenesis process. Thus, cells are provided with complex and efficient mechanisms of DSBs repairing2.
When a DSB occurs, the cell triggers the DNA damage response (DDR) where, together with the MRE11/RAD50/NBS1 complex, ATM or ATR kinases are recruited to activate other proteins that slow down or stop the cell cycle3. An essential target of these kinases is histone H2AX, which is phosphorylated on Ser-139 within a few megabases from the DSBs (namely &#947;H2AX), thereby allowing the recruitment of several repair factors such as, among others, BRCA1 and p53 binding protein 1 (53BP1)3. Later, one pathway among homologous recombination (HR), non-homologous end joining (NHEJ), or single-strand annealing (SSA) is triggered to repair the DSBs4,5. Therefore, 53BP1 is involved in dictating the choice between HR or NHEJ, mainly promoting the activation of NHEJ rather than HR6. Moreover, both the phosphorylated form of H2AX histone and 53BP1 can form foci at the sites of DSBs. As these foci persist until the integrity of the double strand is restored, assessing the appearance/disappearance of &#947;H2AX or 53BP1 foci within a time interval is considered a useful method to evaluate the occurrence and repair of DSBs in a cell system6,7. However, according to the molecular processes above described, since &#947;H2AX and 53BP1 foci are expected to co-localize near the DSBs during DDR8,9, it can be useful to detect concurrently the presence of these markers in a dual immunofluorescence.
Thus, the aim of this manuscript was to evaluate the suitability of the simultaneous quantification of &#947;H2AX and 53BP1 foci to assess the genomic damage induced in human peripheral lymphocytes by the radiomimetic agent bleomycin. Using the same methodology, we also attempted to delineate repair kinetics of bleomycin-induced DSBs according to a previously set up experimental procedure10.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>AlexaFluor 568 goat anti-mouse IgG (&#947;1)</td>
			<td>Invitrogen</td>
			<td>A21124</td>
			<td>53BP1 secondary antibody</td>
		</tr>
		<tr>
			<td>Bleoprim</td>
			<td>Sanofi</td>
			<td></td>
			<td>bleomycin sulfate (mutagen)</td>
		</tr>
		<tr>
			<td>Penicillin-streptomycin solution 100X</td>
			<td>Euroclone</td>
			<td>ECB3001D</td>
			<td>antibiotics for culture medium</td>
		</tr>
		<tr>
			<td>PBS 10X</td>
			<td>Termofisher</td>
			<td>14200075</td>
			<td>Phosphate-buffered saline</td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Euroclone</td>
			<td>EC20180L</td>
			<td>Fetal Bovine Serum for immunofluorescence</td>
		</tr>
		<tr>
			<td>Goat anti-rabbit IgG (H+L) DyLight 488 Coniugated</td>
			<td>Termofisher</td>
			<td>#35552</td>
			<td>&#947;H2AX secondary antibody</td>
		</tr>
		<tr>
			<td>Mouse anti-53BP1 monoclonal antibody</td>
			<td>Merck</td>
			<td>MAB 3802</td>
			<td>53BP1 primary antibody</td>
		</tr>
		<tr>
			<td>Labophot 2</td>
			<td>Nikon</td>
			<td></td>
			<td>Fluorescence microscope</td>
		</tr>
		<tr>
			<td>P-histone H2AX (Ser139) rabbit antibody</td>
			<td>Cell Signaling</td>
			<td>#2577</td>
			<td>&#947;H2AX primary antibody</td>
		</tr>
		<tr>
			<td>Phytohemoagglutinin</td>
			<td>Termofisher</td>
			<td>R30852801</td>
			<td>component of culture medium</td>
		</tr>
		<tr>
			<td>Prolong gold antifade reagent with DAPI</td>
			<td>Cell Signaling</td>
			<td>#8961</td>
			<td>Antifade solution with DAPI for counterstaining</td>
		</tr>
		<tr>
			<td>RPMI 1640</td>
			<td>Euroclone</td>
			<td>ECB9006L</td>
			<td>Culture medium</td>
		</tr>
		<tr>
			<td>Triton-X100</td>
			<td>Sigma</td>
			<td>T9284</td>
			<td>Nonionic detergent for permeabilization</td>
		</tr>
	</tbody>
</table>

dual immunofluorescence of &#947;h2ax and 53bp1 in human peripheral lymphocytes

Double strand breaks (DSBs) are one of the most severe lesions that can occur in cell nuclei, and, if not repaired, they can lead to severe outcomes, including cancer. The cell is, therefore, provided with complex mechanisms to repair DSBs, and these pathways involve histone H2AX in its phosphorylated form at Ser-139 (namely &#947;H2AX) and p53 binding protein 1 (53BP1). As both proteins can form foci at the sites of DSBs, identification of these markers is considered a suitable method to study both DSBs and their kinetics of repair. According to the molecular processes that lead to the formation of &#947;H2AX and 53BP1 foci, it could be more useful to investigate their co-localization near the DSBs in order to set up an alternative approach that allows quantifying DSBs by the simultaneous detection of two DNA damage markers. Thus, this protocol aims to assess the genomic damage induced in human lymphocytes by the radiomimetic agent bleomycin through the presence of &#947;H2AX and 53BP1 foci in a dual immunofluorescence. Using this methodology, we also delineated the variation in the number of &#947;H2AX and 53BP1 foci over time, as a preliminary attempt to study the repair kinetics of bleomycin-induced DSBs.

Data obtained by the fluorescence microscope analysis of peripheral lymphocytes allow us to evaluate three main aspects: the effectiveness of bleomycin treatment in increasing the number of &#947;H2AX and 53BP1 foci (and thus of DSBs) due to its mutagenic effect, at what extent both foci co-localized at the site of DSBs, and the time-course of &#947;H2AX and 53BP1 foci to delineate the repair kinetics of bleomycin-induced DSBs. As expected, a very higher frequency of both &#947;H2AX and 53BP1 foci was observed between un...

Watch this Scientific Journal Video about Dual Immunofluorescence of Î³H2AX and 53BP1 in Human Peripheral Lymphocytes at JoVE.com

Dual Immunofluorescence of &amp;#947;H2AX and 53BP1 in Human Peripheral Lymphocytes

This protocol presents a method to assess the formation and repair of DNA double-strand breaks through the simultaneous detection of &#947;H2AX and 53BP1 foci in interphase nuclei of bleomycin-treated human peripheral lymphocytes.

Dual Immunofluorescence of &#947;H2AX and 53BP1 in Human Peripheral Lymphocytes

Double strand breaks (DSBs) are one of the most severe lesions that can occur in cell nuclei, and, if not repaired, they can lead to severe outcomes, ...

The aim of this manuscript was to evaluate the suitability of the simultaneous quantification of Gamma H2AX and 53BP1 foci to assess the genomic damage induced in human peripheral lymphocytes by bleomycin. Several factors can cause double strand breaks. Cells are thus provided with several repair mechanisms, involving both Gamma H2AX and 53 Binding Protein 1, that can co-localize near the double strand break.After collecting whole blood samples, add 300 microliters of sample to a tube containing 4.7 milliliters of complete medium. Then add five micrograms per milliliter of bleomycin sulfate final concentration. For each sample, set up a negative control.Put the tube in a thermostat at 37 degrees Celsius for two hours. Centrifuge samples at 540 G for five minutes. Then add five milliliters of hypotonic solution to pellet.Then add 400 microliters of pre fixative solution in order to cause hemolysis. Centrifuge samples at 540 G for five minutes, then resuspend pellet in five milliliters of methanol at room temperature for at least 30 minutes to fix the cells. Centrifuge samples at 540 G for five minutes, then resuspend pellet in five milliliters of fixative solution.Repeat this step once more time. Centrifuge again at 540 G for five minutes, then aspire the supernatant leaving enough solution to resuspend pellet. Drop the resuspended cell pellet on the slides.Prepare the two solutions containing the anti-Gamma H2AX and the anti-53BP1 primary antibodies dissolved in blocking solution. Then wash slides two times in PBS 1X. Then keep slides for 30 minutes in blocking solution.Add to each slide 10 microliters of each of the two solutions containing the primary antibodies dissolved in blocking solution. Cover the slides with parafilm. Incubate at four degrees Celsius overnight.After the incubation, perform three washing in PBS 1X for five minutes. Prepare the two solutions containing the DyLight 488 and Alexa Fluor 568 secondary antibodies dissolved in blocking solution. Then add to each slide 10 microliters of each of the two solutions containing the secondary antibodies dissolved in blocking solution.Cover the slides with parafilm and incubate at room temperature for two hours. After this second incubation, perform three washing in PBS 1X for five minutes. Add 2.5 microliters of Antifade solution with DAPI on the cover slips before assembly to counter stain the nuclei.In order to assess foci kinetic, the procedure is the same as now described. The last phase is observation and quantification of foci. Human lymphocytes without Gamma H2AX and 53BP1 foci are shown in A, in B, and in C, human lymphocytes with different amounts of Gamma H2AX and 53BP1 foci are shown.It is observed a low level of foci co-localization. As expected, a very higher frequency of both Gamma H2AX and 53BP1 foci are observed between untreated untreated cells. Also, a large difference is observed in the number of foci of the two markers.The time course of Gamma H2AX and 53BP1 foci over time showed a different behavior although they contribute to the same function. Gamma H2AX and 53BP1 foci analysis has the ability to evaluate the cellular response in either exposure or pathological contexts. However, Gamma H2AX and 53BP1 dual immunofluorescence can lead to underestimate the true frequency of the event.

dual-immunofluorescence-h2ax-53bp1-human-peripheral

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1.1K Views.  University of Pisa. The aim of this manuscript was to evaluate the suitability of the simultaneous quantification of Gamma H2AX and 53BP1 foci to assess the genomic damage induced in human peripheral lymphocytes by bleomycin. Several factors can cause double strand breaks. Cells are thus provided with several repair mechanisms, involving both Gamma H2AX and 53 Binding Protein 1, that can co-localize near the double strand break.After collecting whole blood samples, add 300 microliters of sample to a tube ...