DIFFERENCES IN MUCUS AND SERUM IMMUNOGLOBULIN OF CARP (CYPRINUS-CARPIO L)

Electrophoretic analysis did not reveal clear differences between skin mucus and serum immunoglobulin (Ig) of carp. The majority of both Igs were tetrameric (+/-760 kDa) and composed of 25 kDa light (L) chains and 70 kDa heavy (H) chains, but dimeric and monomeric forms were foun d as well. Monoclonal antibody (mAb) WCI 12 produced from serum Ig app eared to react with the H chain of both molecules. After immunisation of mice with purified mucus Ig, mAbs could be selected that were react ive with mucus Ig only. Two of these mAbs (WCI M1 and WCI M2) were imm unoreactive with the H chain of mucus Ig and not or hardly immunoreact ive with the H chain of serum Ig, indicating differences in the compos ition of the H chains of both molecules. Because WCI M2 appeared to re cognize a carbohydrate determinant, differences seem to occur in the p rotein as well as carbohydrate composition of mucus and serum Ig. Flow cytometric results showed that both mAbs were reactive with the same subpopulation of WCI 12-positive B cells. Immunohistochemical reaction s on cryosections also showed a limited reaction by these mAbs compare d with WCI 12; only epithelium of skin and bile ducts and capillaries in the liver were strongly positive with these mAbs. The presence of m ucus Ig at these locations is discussed. Our results indicate structur al and functional differences between mucus and serum Ig, which may ex plain the mucosal immune responses reported for fish. Such a specific mucosal defense system can be very important for fish, living in a pat hogen-rich environment.