Secretory Immunoglobulin A (sIgA) is an antibody found in mucus, tears, saliva, mother’s milk and other areas. This antibody is very important to your body’s immune defenses. sIgA traps invading bacteria so they pass through the body before causing an infection. sIgA is also an important part of intestinal immune health by keeping pathogens from attaching to the intestinal lining.