T cell subpopulation phenotypes in filarial infections: CD27 negativity defines a population greatly enriched for Th2...

Three-color flow cytometric analysis was used to define surface markers which identify the Th2-type CD4+ cells responsible for the eosinophilia and elevated serum IgE typical of tissue invasive helminth infections. A group of six mAbs to well known cell surface markers were screened for differential expression on CD4+ CD45RO+ lymphocytes from normal individuals (NL; n = 6) and filaria-infected patients (PT; n = 10). The majority of markers were expressed equally by both groups, but the CD4+ CD45RO+ cells in the PTs showed significantly higher levels of expression of HLA-DR than those of NLs (P = 0.014). This CD4+ HLA-DR+ subpopulation was then studied further for its expression of an additional 10 activation and adhesion molecules. CD27 showed a trend for lower intensities of expression on PT CD4+ HLA-DR+ cells than on those of NLs. Analysis of the serum from both NLs and PTs revealed that PTs had significantly higher levels of soluble CD27 and CD25 (IL-2R) in the serum than NLs (P < 0.01 and P = 0.022 respectively) indicating a general state of immune activation and differentiation. Functional analysis of the CD4+ HLA-DR+ and the CD4+ CD27- subpopulations revealed that the CD4+ HLA-DR+ cells produced significantly higher levels of IL-5 than the CD4+ HLA-DR- cells (P = 0.04), and the CD4+ CD27- cells produced significantly higher levels of both IL-4 and IL-5 than the CD4+ CD27+ cells (P < 0.05 and P < 0.001 respectively). Thus, while the CD4+ CD27- and CD27+ subpopulations contain Th1 and Th0 cells, only the CD4+ CD27- population contains the Th2 cells (producing both IL-4 and IL-5).