Novel differences in the characteristics of spleen and peripheral blood lymphocytes activated by anti-immunoglobulin

Alkaline phosphatase activity is expressed only in B lymphocytes committed to proliferation

Alkaline phosphatase (APase) activity was measured in murine splenic lymphocytes stimulated with the T lymphocyte mitogens phytohemagglutinin (PHA) and Concanavalin A (Con A) and the B lymphocyte mitogens lipopolysaccharide (LPS) and anti-immunoglobulin (anti-Ig). APase activity was found to be enhanced specifically in mitogen-stimulated B lymphocytes, but not in T lymphocytes. This enhancement starts around 8 h after stimulation with a mitogen. With soluble anti-Ig it was observed that the B cells enter G1 phase as assessed by RNA synthesis and blast transformation. However, these cells fail to synthesize DNA and also do not show any increase in APase activity. When the same anti-Ig coupled to Sepharose was used as a stimulator, cells synthesized DNA and also showed significant increase in APase activity. When hydroxyurea was added, the enhancement in APase activity by the mitogen was not diminished although the cells failed to synthesize DNA. These observations indicate that APase activity is enhanced only in activated B cells committed to proliferation.

Fate of surface immunoglobulin during induction of lymphocyte proliferation

The modulation of immunoglobulin on the surface of rabbit B lymphocytes by goat antibodies with specificity for rabbit surface membrane immunoglobulin or by such goat antibodies covalently linked to Sepharose was studied in relation to the proliferative response to these agents. Although the induction of DNA synthesis was greater in the presence of Sepharose-linked antibody than in the presence of free antibody, modulation of surface membrane immunoglobulin was induced with free but not with Sepharose-linked antibody. Thus, in the presence of free antibody the surface membrane immunoglobulin content of cells was rapidly decreased and remained at a low level throughout the culture period, whereas the surface immunoglobulin content of cells incubated with Sepharose antibody was essentially unaltered. The surface immunoglobulin lost from cells incubated with free goat antibodies reappeared slowly upon further incubation in culture medium devoid of antibody, and such reappearance of rabbit surface membrane immunoglobulin was inhibited by puromycin. Upon culture with Sepharose-linked antibody the surface membrane immunoglobulin content of B cells was unaffected by puromycin. This result was interpreted as indicating that surface membrane immunoglobulin loss followed by reappearance does not occur. Lastly, the linkage of surface membrane immunoglobulin to cytoskeletal elements induced by free antibody was not induced by Sepharose-linked antibody as judged from differences in detergent solubilization characteristics. Possible mechanisms to account for these differences in surface membrane immunoglobulin modulation as they relate to the proliferative response are considered.