Multiple heavy chain isotypes on the membrane of the small B lymphocytes in human blood.

Small lymphocytes from adult human blood were examined for the presence of membrane-associated alpha, gamma, delta and mu Ig isotypes by means of a direct immunofluorescence technique. Since less than 10% of the small lymphocytes in blood are B cells as defined by positive reactivity with an anti-Fab conjugate, our experiments were performed on a T cell-depleted fraction in which about 80% of the small lymphocytes were B cells. With the two-wavelength immunofluorescence method, all of the double-isotype combinations were found. The percentage of cells bearing more than two isotypes was deduced. The delta mu and the alpha delta mu combinations were the most common, as previously found on tonsillar lymphocytes. In contrast with the tonsils, no lymphocytes bearing only delta were observed and the proportions of alpha gamma- and alpha gamma mu-bearing lymphocytes were very small. The presence of lymphocytes bearing four isotypes could practically be excluded.

Presence of multiple isotypes on the surface of human tonsillar lymphocytes.

Formaldehyde-fixed small lymphocytes from human tonsils were investigated for the presence of the Ig heavy chain class isotypes alpha, gamma, delta and mu on their membranes by means of a direct immunofluorescence technique. About 50% of the small lymphocytes were defined as B cells with an anti-Fab antiserum. Most of the B lymphocytes carried more than one isotype on their membrane, and all combinations of two isotypes were observed. The existence of three or four isotypes on the membrane of individual lymphocytes was deduced. The sIgD, sIgM and sIgA, sIgD, sIgM combinations were the most common. The isotypes were present as separate molecules since they showed independent distribution patients undeesent as separate molecules since they showed independent distribution patterns under capping conditions.