IgG on human blood lymphocytes studied by immunofluorescence.

Surface immunoglobulins (sIg) on human blood lymphocytes were identified by immunofluorescence (IFL) after staining with conjugated F(ab'2) fragments of the anti-Ig antibodies. A large fraction (approximately 20%) of freshly isolated lymphocytes was found to carry sIgG. Polyclocal IgG, which was present on Fc-receptor-bearing lymphocytes, could be removed by incubation and repeated washings only at 37 degrees C. Lymphocytes treated at 37 degrees C expressed the same percentage of sIg+ cells in direct IFL when F(ab')2 fragments of the antibody was used as when undigested aggregate-free IgG antibody was used. Indirect IFL using F(ab')2 fragments in both steps yielded similar sIg+ values. However, much higher percentage of cells carried sIg when undigested antibody was included in one of the steps. The results suggest that incubation and washing at 37 degrees C and the use of F(ab')2 fragments of the antibodies are important to eliminate absorbed sIgG and to avoid absorption of IgG during the staining procedure, thus preventing overestimation of the number of sIg+ B lymphocytes identified by IFL.