The LFA-1 antigen in human B lymphocyte activation.

Human tonsil B cells include a subpopulation (30 per cent) of cells which lack LFA-1 antigen. Activation of tonsil B cells by culture with anti-IgM and interleukin-4 led to an increase in staining intensities and in the proportion of cells staining, until by 48 h the majority of B cells were positive. Culture of activated cells with low-molecular weight B cell growth factor, which induces a proportion of cells to proliferate, led to a minor further increase in expression of the LFA-1 antigen. Inclusion of a monoclonal antibody against the LFA-1 beta chain in culture did not affect either proliferation or immunoglobulin secretion. The expression of LFA-1 by B cells thus changes as B cells are activated, perhaps reflecting the changing requirements of B cells for interaction with other cells and tissue components. On the other hand, our results did not provide any support for the idea that the LFA-1 antigen is directly involved in the interaction of B cells with lymphokines which control proliferation and differentiation.

B prolymphocytic leukemia cell lines: phenotype and response to B cell differentiation factor.

Three recently-derived cell lines of prolymphocytic leukemia origin were studied. The phenotype of the cells, analysed in terms of expression of immunoglobulin and other B cell maturation markers, indicates that the cells are mature B lymphocytes close to the plasma cell stage of differentiation. All three cell lines secrete IgM, and two of the three lines respond to B cell differentiation factor with an increased secretion of IgM.

B lymphocyte/carcinoma antigen (BLCa): functional study in B cells.

BLCa is an antigen expressed on the surface of B lymphocytes and certain carcinomas. In this study we have demonstrated that BLCa is distinct from known B cell antigens classified by 'clusters of differentiation' (CD). In particular, the monoclonal antibody MA6, which identifies BLCa, can be distinguished from antibodies of the CDw40 group, which detect an antigen of similar molecular weight expressed also on B cells and certain carcinomas. The expression of BLCa on B cells was measured as tonsil B cells were activated (by anti-Ig and interleukin-4 (IL-4)), induced to proliferate (by low molecular weight B Cell Growth Factor (LMW-BCGF), and induced to differentiate (by B Cell Differentiation Factor, BCDF). Expression of BLCa increased in response to LMW-BCGF. The effect of inclusion of MA6 antibody in cultures with the B cell stimuli was also investigated. MA6 showed an anti-proliferative effect which was antibody-dose dependent, but did not otherwise inhibit or co-operate with anti-Ig. IL-4, LMW-BCGF or BCDF.

The p24 leucocyte membrane antigen: modulation associated with lymphocyte activation and differentiation.

Monoclonal antibodies of the CD9 cluster recognize a 24 kD protein (p24) found on platelets and endothelium, and expressed by lymphocytes at restricted stages of maturation and activation. In this study, we explore the possibility that p24 is involved in the response of lymphocytes to signals delivered by lymphokines. p24 is expressed only very weakly by resting B lymphocytes. We found no increase in expression when cells were activated with anti-immunoglobulin together with interleukin-4, or induced to proliferate by low-molecular weight B cell growth factor (LMW-BCGF). Culture of activated B cells with B cell differentiation factor was associated with an increased mean expression of p24. In cells from a patient with chronic lymphocytic leukaemia (CLL), culture with LMW-BCGF up-regulated p24 expression. Resting T cells (p24-negative) were induced to express p24 strongly when activated with antibody against CD3. CD9 antibody did not modulate B or T cell responses to activation stimuli. The results suggest that the p24 molecule is not involved in the primary interaction of cells with lymphokine, but rather may be involved in a secondary reaction, such as ion flux, which follows as a consequence of the action of lymphokines on cells.