PHYSIOLOGY OF IgD

Classic studies by Rowe et al . (1) in the human and by Vitetta and coworkers (2) in the mouse have established that IgD is a major membrane immunoglobulin . This has led to a variety of studies and speculation regarding its biological function . Based upon the effect of anti-IgD on the in vitro primary response, Cambier et al . (3) suggested that the presence of IgD on the cell surface was critical for responses to thymus-dependent but not thymus-independent antigens . Prolonged in vivo treatment of mice with anti-IgD, starting at birth, was reported by Layton et al . (4) to result in a decrease in the incidence of IgD positive cells, accompanied by a depression in the secondary indirect plaque-forming cell, (PFC)i response . In contrast, Bazin et al . (5) found that treatment with antiserum to IgD from birth led to little or no decrease in any of the immunoglobulin classes except for IgE, which was markedly reduced . IgE antibody responses were also depressed . As in the case ofthe other immunoglobulin classes, allelic exclusion has been shown to exist for IgD (6, 7) . The availability of monoclonal allotype-specific antibody to IgD allows the investigation of the effects of anti-IgD in allotype heterozygous mice, with restriction ofthe effects limited to one halfof the B cell population . Comparison with the alternative allelic products permits a sensitive study of the role of IgD in immune responses with an ideal internal control . Furthermore, anti-IgD treatment of heterozygous or of homozygous mice might provide a clue to phenomena of internal balance and compensation (regulation) within an immune system . We therefore decided to re-investigate several aspects of the effects of anti-IgD on the immune system : (a) to compare the effect of anti-delta suppression in homozygous and heterozygous animals ; (b) to determine whether IgD suppression is linked to the suppression of the corresponding IgG allotypes ; and (c) to determine the effect of functional inactivation of all delta-positive cells on the development of germinal centers and on memory cell generation .