Which is true about immunoglobulins?

(D) All of the above # IgA has two subclasses (lgA1 and lgA2) and can exist in a dimeric form called secretory IgA (slgA). In its secretory form, IgA is the main immunoglobulin found in mucous secretions, including tears, saliva, colostrum and secretions from the genitourinary tract, gastrointestinal tract, prostate and respiratory epithelium.> It is also found in small amounts in blood. Secretory component of slgA protects the immunoglobulin from being degraded by proteolytic enzymes, thus slgA can survive in the harsh gastrointestinal tract environment and provide protection against microbes that multiply in body secretions.IgE is mainly found in extracellular fluids only.