Research progress in molecular biology of fish immunoglobulin D

Immunoglobulins are the primary mediators of the humoral immune response in fish. Studies of immunoglobulins in fish are particularly important for the immunological control of fish diseases. While immunoglobulin D (IgD) was first discovered in 1965, it remains the least understood member of the antibody family. During evolutionary development from fish to humans, IgD has developed critical immunological functions. However, these immunological functions are not well understood. There are two forms of IgD, membrane IgD (mIgD) and secreted IgD (sIgD). sIgD and mIgD are formed by B lymphocytes through different splicing modes. In this paper, IgD’s structure and formation process in fish, the distribution characteristics of IgD on B cells, the mediated signaling pathways, and the functions of IgD are reviewed.