Western blotting performed using human anti-IgA secondary antibody showed that there were eight surface protein bands of Shigella flexneri strain SF480 that only reacted with Shigella flexneri infection serum (Table 2 lane 1 to lane 3) and did not cross-react with other infection sera (Table 2 lane 4 to lane 9). This evidence concerns the gene CD79A and infection.