Presence of IgM in cutaneous mucus, but not in gut mucus of Atlantic salmon, Salmo salar. Serum IgM is rapidly degraded when added to gut mucus

In the first part of this study, cutaneous mucus of Atlantic salmon (Salmo salar) was shown to contain IgM, i.e. molecules composed of approximately 7 2 and 27 kDa subunits and reactive with polyclonal antisera and monoclonal antibodies made against serum IgM. Attempts to detect IgM-like molecules in gut mucus were negative, indicating the IgM is present, at best, in very s mall amounts. The degradation of serum IgM in mucosal secretions was examin ed in the second part of this study. Purified IgM from serum was rapidly di gested in gut mucus at 4 degrees C. Intermediate 58, 52, 38, 35, 33 and 18 kDa breakdown fragments appeared when analysed in immunoblots. The transien t fragments were further degraded to small fragments. HPLC analysis showed that only half of the added serum IgM was intact after 30 min of digestion, and after 4 h intact IgM could not be detected. Serum IgM was not degraded in cutaneous mucus, even after 17 h of incubation. (C) 2001 Academic Press .