Physiology of IgD IX. Effect of IgD on immunoglobulin production in young and old mice

Weekly i.p. injections of IgD from birth in (SJL X BALB/c)F1 mice were found to accelerate the development of IgG- and IgA-secreting cells and to increase the numbers of Ig-secreting cells of all isotypes in 17-28-day-old mice, but not in 7-10-day-old mice. Similarly, repeated weekly injections of IgD in normal adult BALB/c mice increased the numbers of reverse plaque-forming cells/spleen for all isotypes studied, including IgM, IgG1, IgG2, and IgA, but not for IgD itself. No such effect was observed in IgD-treated aged (20 months old) BALB/c mice. The absence of an effect of IgD on Ig secretion appeared to correlate with a lack of induction of receptors for IgD on T cells of the host, both in 7-10-day-old and in aged mice. In 7-10-day-old mice this lack of induction appeared due to their very low numbers of L3T4+ T cells. A comparison was made between the effect of a single injection of IgD or lipopolysaccharide (LPS) on numbers of Ig-secreting cells in the spleen determined 1-7 days after injection. Both agents caused increases, but the increase in IgM-producing cells was much greater after LPS (day 4), while IgD caused a relatively greater increase in IgG2 and IgA (days 4-7). Increases in IgG1 and IgG3-producing cells induced by LPS and IgD were of similar magnitude (days 6-7). IgD production, however, was not increased. The number of cells producing antibody of anti-trinitrophenyl (TNP) specificity was enhanced by LPS (day 4), but not by a single injection of IgD, although more than one injection of IgD caused a significant increase in anti-TNP-producing cells above background. LPS, but not IgD, caused B cell proliferation in vitro in the presence or absence of gamma-irradiated T delta cells. However, in vivo, IgD injections caused a significant increase in the percentage of lymphoid follicles with germinal centers in lymph nodes from 17-21-day-old and normal adult mice, but not in 7-10-day-old or aged mice. Such an effect was also absent in 24-28-day-old mice, where germinal center development, even in untreated mice, was very high.