Final answer:
IgA protects tissues primarily in conjunction with E. complement proteins, not by functioning directly with other immunoglobulins. It is secreted as a dimer in areas.
Step-by-step explanation:
In the context of how IgA functions to protect the tissues, it's important to note that IgA operates mainly with the help of complement proteins, which can be activated by the Fc portion of antibodies to aid in the defense against pathogens. Unlike IgM, which forms pentamers, or IgG, which is the main blood antibody and can cross the placenta, IgA is secreted mostly as dimeric molecules linked with a J chain, primarily in mucosal areas. IgA does not function directly with other immunoglobulin classes such as IgG, IgM, IgE, or IgD to protect the tissues; instead, it has a unique role in neutralization at mucosal surfaces and is able to recruit complement proteins to fight off pathogens.
IgA functions with IgM, IgG, IgE, and complement proteins to protect the tissues. IgM and IgG are involved in the primary and secondary immune responses, respectively. IgE is responsible for allergic responses, and complement proteins enhance the immune response. T lymphocytes, on the other hand, play a role in cell-mediated immunity.