Preferential production of IgA antibodies by spleen fragments immunized and maintained in vitro.

Primary immune responses were induced with a hapten conjugate of Ficol (NIP38-Ficoll) in cultures of mouse spleen fragments. The production of anti-NIP antibodies and mouse immunoglobulins IgA and IgG was monitored by solid-phase radioimmunoassays. Cultures produced IgA and IgG without any stimulation. IgA at a rate of c.60ng/mg of wet tissue per day throughout the 10-day culture period. Background production of IgG gradually declined from almost 1000 ng/mg/day at the beginning to 100 ng/mg/day at the end. Immunization modestly reduced the decline of the IgG production. It increased the production of IgA fourfold between days 6 and 8. It induced an antibody production that had its peak between days 6 and 8. Up to 50 ng of anti-NIP antibody was produced during this period per mg of wet tissue per day. Of this antibody 75-90% was IgA. When the same antigen was injected into mice, more than 75% of anti-NIP antibodies detected in their sera on day 8 were IgG. One cause of the high ratio of IgG/IgA antibodies detected in their sera on day 8 were IgG. One cause of the high rate of IgG/IgA antibodies in vivo is the efficient elimination of oligomeric IgA by the liver. Another possible cause is that the production of IgA is less sensitive than the production of IgG to the adverse conditions of the culture.