Answer C) Interleukin-5
The B cells observed by the investigator have differentiated by isotype switching into plasma cells that secrete IgA, which plays a key role in mucosal immunity.
IgA antibodies would be most expected to prevent pathogen attachment to mucous membranes. While in the germinal center of lymph nodes, mature naive B cells express IgM and IgD.
When their CD40 receptors are exposed to cytokines secreted by T cells, these B cells undergo class switching to plasma cells that are capable of secreting IgA, IgG, or IgE.
The heavy chain constant region (Fc region) is changed, while the heavy chain variable region (specific to the antigen) remains the same.
The cytokine that changes the type of immunoglobulin produced by a mature B cell from IgM to IgA is IL-5, which is secreted by Th2 lymphocytes.
IL-10 is produced by Th2 lymphocytes and can trigger class switching to IgG. However, it is primarily known as an anti-inflammatory factor that reduces the activity of Th1 lymphocytes, macrophages, and the inflammatory NF-?B pathway. Furthermore, IgG binds complement.
IL-2 is responsible for cell-mediated immunity, promoting T cell differentiation and the proliferation of memory and effector T cells following the initial presentation of an unknown antigen. However, it is not involved in B-cell class switching.
IL-4 secreted by Th2 lymphocytes triggers B-cell class switching from IgM to IgG and IgE. However, neither of these antibodies would typically be found in the mucosa. Furthermore, IgG fixes complement.