DEPENDENCE OF LYMPHOCYTE SURFACE IG ON CONTINUOUS POLYCLONAL ACTIVATION

  • 1 January 1979
    • journal article
    • research article
    • Vol. 37  (4) , 731-742
Abstract
It was previously shown that most rabbit splenic B [bone marrow-derived] cells cultured in a medium supplemented with 5% autologous serum require continuous polyclonal stimulation to maintain detectable amounts of surface Ig [immunoglobulin]. In the absence of this stimulation B [bone marrow-derived] cells shed but do not replace their surface Ig. This paper investigates the mechanism responsible for the loss or maintenance of surface Ig. The addition of inhibitors of mRNA and protein synthesis to the cell cultures completely abolished the Ig maintenance effect provided by the mitogen thereby suggesting that it did not act by freezing the membrane Ig but rather by continuously stimulating resynthesis. Moreover, by labeling the surface Ig with 125I-labeled Fab anti-allotype antibody it was shown that the maintenance of surface Ig by mitogen stimulation was due to the turnover of surface Ig. The cells shed and replaced their surface Ig with a half-life of about 2 h only when mitogen was present but shed without replacing the surface Ig in the absence of mitogen. Also, the B cell mitogens, SM [streptococcal mitogen] and LPS [lipopolysaccharide], were able to maintain surface Ig even at extremely small concentrations while the T [thymus-derived] cell mitogens, Con [concanavalin] A and PHA [phytohemagglutinin], failed to do so at any concentration, suggesting that direct stimulation of B cells was needed to maintain surface Ig. When spleen cells were cultured in crowded conditions in the absence of mitogen they did not lose their surface Ig; under these conditions it appeared that a factor associated with the macroglobulin fraction is induced and acts in the same manner as a B cell polyclonal activator to maintain the turnover of surface Ig. Such a factor may actually function in vivo since lymphocytes are in very close contact in the lymphoid organs. Rabbit B lymphocytes shed and replace their surface Ig with a half-life of about 2 h. The replacement, but not the shedding of surface Ig, is dependent on continuous exogenous or endogenous polyclonal activation.