Lymphocyte phenotyping by fluorescence microscopy and flow cytometry: results in homosexual men and heterosexual...

Absolute numbers of peripheral blood T3, T4 and T8 positive cells from 15 homosexual men and concurrent controls were determined by fluorescence microscopy (FM) and by a fluorescence-activated cell sorter (FACS). A significant difference in the number of positive cells was observed between FM and FACS in the control group for all three monoclonal antibodies and for the T4/T8 ratio. FACS methodology yielded a lower number of T4 positive cells and a lower T4/T8 ratio in the homosexual subjects. Two homosexual men had normal T4/T8 ratios by FM but were found to have low ratios by FACS. The reasons for the disparate results obtained by the two methods are unclear, but such findings are important to bear in mind when evaluating male homosexuals for immunologic abnormalities.