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 × 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 IgG_l 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 γ ‐irradiated Tδ 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.