CD3 bright lymphocyte population reveal γδ T cells

Background: In routine CD3/CD4/CD8 T-cell analysis, a CD3 bright population of lymphocytes is frequently observed. The aim of the present study was to identify the immunological significance of such CD3 bright lymphocytes. Methods: We analyzed samples from 31 healthy adult volunteers, 78 human immunodeficiency virus (HIV)-positive, and 78 renal transplanted patients. Results: A clearly distinct CD3 bright (frequently CD4(-)/CD8(-)) T-cell fraction was observed in 84% of donors and was directly correlated with the fraction of gammadelta T cells (r(2) = 0.64). CD3 overexpression on gammadelta T cells was confirmed by a combination of monoclonal antibody staining (CD3-ECD, gammadeltaTCR-FITC, and alphabetaPTCR-PE-Cy5) or immunomagnetic purification of gammadelta T cells (i.e., MdFI 20 vs 8.86). The gammadelta T cells expressed COB polypeptide chains (alpha and beta) in all possible combinations. The largest proportion, surprisingly, were cells expressing CD8betabeta homodimers (43.8 +/- 16.5%). CD8alphaalpha homodimers were expressed on 14.2% (+/- 12.3) of total gammadelta T cells, whereas CD8alphabeta heterodimers were expressed on 12.2% (+/- 7.5). We also observed a bimodal distribution of the intensity of CD3 fluorescence of 78 T cells in immunocompromised patients with a threshold at 105 cell/mul. CD3 bright gammadelta T cells were more frequently observed in HIV patients (29%) compared with renal transplant patients (11%) and healthy donors (3%; chi (2) test: P = 0.0007). Conclusions: The simple observation of a CD3 bright T-cell subset on CD3/CD4/CD8 routine analysis suggests a high gammadelta T-cell fraction and, in our opinion, should he followed by a complementary analysis to determine precisely the number of gammadelta T cells and to identify their CD8alpha/beta phenotype. When CD3 bright T cells/mul were more than 40%, high gammadelta T cells were detected in more than 87% of cases, with a specificity of 76%. Occasionally, the CD3 bright subset appeared to be strongly homogeneous, suggesting an oligoclonal proliferation that could possibly reveal a chronic localized stimulation or an early lymphoproliferative disorder. Because the gammadelta T cells have interesting immunological peculiarities, the clinical significance of their quantitative abnormality should be clarified in diseases such as HIV, organ transplantation, autoimmunity and lymphoma. (C) 2004 Wiley-Liss, Inc.