Preferential Production of IgA Antibodies by Spleen Fragments Immunized and Maintained in Vitro

Abstract

Primary immune responses were induced with a hapten conjugate of Ficoll (NIP38[4-hydroxy-3-iodo-5-nitrophenyl acetyl]-Ficoll) in cultures of mouse spleen fragments. The production of anti-NIP antibodies and mouse IgA and IgG was monitored by solid-phase radioimmunoassays. Cultures produced IgA and IgG without any stimulation, IgA at a rate of .apprx. 60 ng/mg of wet tissue per day throughout the 10 day culture period. Background IgG production gradually declined from almost 1000 ng/mg per day at the beginning to 100 ng/mg per day at the end. Immunization slightly reduced the decline in IgG production. It increased IgA production 4-fold 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/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 in vivo is the efficient elimination of oligomeric IgA by the liver. Another possible cause is that IgA production is less sensitive than IgG production to the adverse culture conditions.