Basal immunoglobulin serum concentration and isotype distribution in relation to the polygenic control of antibody responsiveness in mice

Serum Ig concentration and isotype distribution were determined in the high (H) and low (L) responder lines selected for antibody response to complex immunogens. Data were recorded in normal and postimmunization sera from the H and L lines produced by five independent selective breedings (selections I, 11, III, IV, and V). Ig levels were much higher in H than in L mice of all the selections. In four selections this interline difference increased further after immunization with the selection antigens. This is in agreement with the general effect of the polygenic control of antibody responses operating in H and L lines. The Ig isotype profiles of normal sera were different in each line; however, similitudes were noticed between H and L lines in selections I and If. In contrast, in selections III, IV, and V a similar interline difference was observed: the lack of IgG2a isotype in L lines only. After immunization there were minor alterations of the isotype profiles except in the H lines of selections III and IV, in which a clear inverse modification of IgG₁ and IgG_2a proportions occurred. The characteristic pattern of each selection may be partially dependent on isotype-restricted regulatory effects in relation to the immunization procedure used for selective breeding.