Demonstration of surface membrane immunoglobulin on L lymphocytes by the mixed antiglobulin rosetting reaction (MARR) and by the direct antiglobulin rosetting reaction (DARR).

Various preparations of human peripheral blood lymphocytes were examined for the presence of membrane-incorporated immunoglobulin (Ig) molecules using the direct antiglobulin rosetting reaction (DARR) and/or the mixed antiglobulin rosetting reaction (MARR). In an initial study, 97% of lymphocytes depleted of sheep erythrocyte (E) rosette-forming cells were found to be Ig positive by the MARR. This suggests that the majority of E rosette-negative lymphocytes are Ig-bearing B lymphocytes. Since most investigators divide E rosette-negative lymphocytes into an Ig-positive or B-cell population and an Ig-negative or null-cell population, it was decided to study further a well defined null-cell subset. Lymphocytes with membrane-labile IgG markers or L lymphocytes are reported to be E rosette negative, Ig negative by direct immunofluorescence (DIF), C3 receptor negative and Fc receptor positive. L lymphocytes were separated from DIF-positive B cells then tested for the presence of surface Ig, approximately 80% of L lymphocytes were found to be Ig positive with both the MARR and the DARR. Comparison of gamma, alpha and mu heavy chain determinants on both DIF-positive and L lymphocytes indicated that Ig isotypes are similar on both cell types. These various findings suggest that most L lymphocytes are of B-cell lineage.