To assess the humoral immunological responses at the subclass level in
shigellosis, specific antibody responses against Shigella dysenteriae 1
lipopolysaccharide (LPS), S. flexneri Y LPS, invasion plasmid-coded
protein antigens (Ipa), and
Shiga toxin were analyzed. Antibody responses of 41 patients with S. dysenteriae 1
infection (
SDIP) and 15 patients with S. flexneri
infection (SFIP) were compared with those of controls (n = 40). The levels of total
immunoglobulin G (
IgG),
IgA,
IgM, and
albumin in serum and stool samples were analyzed. In addition, total
IgA (t-
IgA), secretory IgA (s-
IgA), and
antigen-specific s-
IgA in fecal samples were analyzed to evaluate the specificities and magnitudes of the mucosal immune responses. By comparing the relative increases in optical density for each
IgG subclass separately, it was determined that the anti-LPS (homologous) response initially increased in the order
IgG2 >
IgG1 >
IgG3 >
IgG4 and that this order changed to
IgG2 >
IgG3 >
IgG1 >
IgG4 later in the disease. The
IgG subclass response against
protein antigens initially showed the order
IgG1 >
IgG3 >
IgG2 >
IgG4, which changed to
IgG3 >
IgG1 >
IgG2 >
IgG4 later in the disease. A significant increase in the proportion of
IgA2 among t-
IgA compared with that in controls was seen in both
SDIP and SFIP, while significant changes in the proportions of
IgG1 and
IgG2 among t-
IgG compared with controls was seen only in
SDIP. The anti-LPS
IgA2 response was more prominent in
SDIP than in SFIP. We found an early peak of
antigen-specific s-
IgA in fecal samples, with a shorter duration than the corresponding response in serum samples. The simultaneous increase of serum
IgA, fecal t-
IgA, and s-
IgA in
SDIP compared with those in SFIP suggests that there is a massive increase in the local
IgA production, giving an increase in systemic
IgA concomitant with an extensive gut mucosal
inflammation leading to an increased loss of
albumin,
IgG, and
IgA with a high ratio of t-
IgA to s-
IgA.