We studied the function of submandibular lymph nodes (MLN) in the oral mucosa immune system as compared with that of inguinal lymph nodes (ILN) in the cutaneous one. Primary IgM, IgG and IgA antibody responses in MLN to sheep red blood cells (SRBC) as a model antigen given submucosally occurred more extensively than those in ILN to the antigen injected subcutaneously. Particularly, definite IgA synthesis was seen in MLN but not in ILN. This IgA synthesis was shown to be originated locally in oral submucosal lymphoid tissue or MLN but not in gut-associated lymphoid tissue (GALT). This suggested that the oral mucosal tissue including MLN acts like Peyer’s patches in GALT for IgA synthesis. When mice were administered with SRBC and bacterial lipopolysaccharide (LPS) submucosally, the adjuvant effect of LPS was only observed on the capacity of MLN cells for secondary antibody response in vitro. This contrasted to the marked augmentation by LPS of both the primary antibody response in ILN and capacity for in vitro secondary antibody response of ILN cells of mice given SRBC and LPS subcutaneously. The radioactivities detected in the local lymph nodes and other tissues of mice given 51Cr labeled SRBC submucosally or subcutaneously were comparable with each other. MLN, however, contained more Ig+/B220+ B cells and less Thy1+/Ly-1+ T cells than ILN did, and the L3T4/Ly-2 ratio of T cell subpopulations in MLN was lower than that in ILN. Partially corresponding to this observation, the B cell-dependent area was developed more extensively in MLN than in ILN. This difference in cellular composition and organization might in part explain the reason why MLN and ILN display distinct modes of response and sensitivity to the action of LPS.
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