The mucosal immune system provides the initial immunological barrier against most pathogens which invade organism through mucosal system, and secretory IgA antibodies mediate primary defense functions in mucosal immune system.We have demonstrated that measles virus matrix protein specific IgA antibody can interact with newly synthesized matrix protein during IgA transport through the epithelial cells, and neutralize virus replication intracellularly, implying that besides surface proteins which were traditionally regarded as targets antigens, highly conserved non-surface proteins can also be effective target antigens.