Antigen-specific IgA response of NALT and cervical lymph node cells in antigen-primed rats

Using antigen-primed rats, we examined the occurrence of antigen-specific antibody forming cells in mononuclear cells (MNC) of nasopharynx associated lymphoid tissues (NALT) and cervical lymph nodes (CLN) following in vitro stimulation with lipopolysaccharide (LPS), cytokines and antigen using the ELISPOT assay method. The rats were immunized with ovalubumin (OVA) by intraperitoneal injections, then by daily intranasal boostering for 2 weeks. In the nasal lavage fluid, the level of OVA-specific IgA antibody was higher and that of OVA-specific IgG antibody was lower than those antibodies in the serum. Following incubations, most of the IgA spot forming cells (SFC), but only 5-10% of IgG SFC were proved to be antigen-specific in the NALT and CLN MNCs. Following LPS stimulation, both the antigen-specific IgA and IgG SFCs increased 1.5- to 2-fold in the NALT MNC. However, following OVA stimulation, the antigen-specific IgA SFC increased 6- to 8-fold, which was remarkably higher than the antigen-specific IgG SFC. The changes of the antigen-specific immunoglobulin SFCs in the CLN MNC following the antigen stimulation were similar to those in the NALT MNC. These Endings suggested that NALT might be one of the induction sites for antigen-specific IgA responses in rats.