Development of a Monoclonal Antibody Specific to the IgM Heavy Chain of Bighead Catfish (Clarias macrocephalus): A Biomolecular Tool for the Detection and Quantification of IgM Molecules and IgM+ Cells in Clarias Catfish.

Catfish is a commonly-cultivated freshwater fish in Thailand and many Southeast Asian countries. The molecular data obtained for the IgM heavy chain (IgMH) of catfish have been useful for distinguishing monoclonal antibodies (mAbs). A mAb specific to Cµ1 of the IgMH of catfish (IgMHCµ1 mAb) was developed in a rabbit model using sequence information from bighead catfish (Clarias macrocephalus). The IgMHCµ1 mAb strongly recognized the IgM heavy chain of the tested catfish, namely, bighead catfish, African catfish (Clarias gariepinus) and their hybrid (C. macrocephalus × C. gariepinus), in immunological Western blot analysis and competitive ELISAs. Additionally, the IgMHCµ1 mAb successfully recognized IgM+ cells by detecting IgM molecules in both secreted and membrane-bound forms in peripheral blood leukocytes (PBLs). The IgMHCµ1 mAb was further used to quantify the percentage of IgM+ cells among PBLs through flow cytophotometry. The IgM+ cell percentages of healthy bighead catfish, African catfish and their hybrid were 38.0-39.9%, 45.6-53.2%, and 58.7-60.0%, respectively. Furthermore, the IgMHCµ1 mAb showed no cross-reactivity with the IgM of zebrafish. These findings suggest that this mAb can be used as an immunological tool for monitoring the health, immune status, and immune development of cultivated Clarias catfish.