Any of various lymphoid tissues or organs that protect the mucosal surfaces, including the digestive tract (see gut-associated lymphoid tissue), respiratory tract (see bronchial-associated lymphoid tissue), eyes, and reproductive tract. This network constitutes the mucosal immune system and overall contains about half of all the body’s lymphocytes, emphasizing its importance in immune defence. Plasma cells of MALT produce chiefly IgA-type antibodies, which are found widely in mucosal secretions.