Late events in B cell activation. Expression of membrane alkaline phosphatase activity.
Alkaline phosphatase (APase) has been previously described as a membrane marker correlating with B cell proliferation after stimulation by selected B cell mitogens. We have found, however, that the appearance of B cell membrane APase correlates more closely with differentiation than with proliferation. This conclusion has been drawn from the following observations: 1) APase activity appears well after peak B cell thymidine uptake, 2) mitogens which stimulate only B cell proliferation (Salmonella typhimurium mitogen) fail to induce expression of the enzyme, and 3) when proliferation of mitogen-activated B cells is inhibited, APase activity is not suppressed and may even be augmented. In addition to membrane expression, APase is also spontaneously shed into the surrounding milieu, perhaps as a result of endogenous phospholipase activity. By using a group of well-characterized inhibitors, the APase activity was shown to belong to class I (similar to the bone/liver/kidney class). Because APase always appears in differentiating but not proliferating cells, we would propose that the enzyme appearance is a late marker of B cell activation, associated with cell progression to differentiation and consequent IgM synthesis.
Burg
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Veterans Administration Medical Center, Iowa City 52241.
Feldbush
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D000469:Alkaline Phosphatase / Q000145:classification / Q000378:metabolism*; D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology* / Q000276:immunology / Q000378:metabolism; D002469:Cell Separation; D007075:Immunoglobulin M / Q000096:biosynthesis; D007700:Kinetics; D008213:Lymphocyte Activation; D008565:Membrane Proteins / Q000145:classification / Q000378:metabolism*; D051381:Rats; D011917:Rats, Inbred Lew; D012995:Solubility; D013601:T-Lymphocytes / Q000201:enzymology; D013936:Thymidine / Q000378:metabolism
D007075:Immunoglobulin M; D008565:Membrane Proteins; D000469:Alkaline Phosphatase; D013936:Thymidine