Development of the natural response of immunoglobulin secreting cells in the pig as a function of organ, age and housing

We analysed the development of the natural immunoglobulin-secreting cell (I g-SC) response in systemic- and mucosal-lymphoid tissues of specified patho gen free pigs between 1 and 40 weeks of age. As antigen exposure may influe nce the development of the Ig-SC repertoire we also compared the frequencie s of Ig-SC in various lymphoid tissues of 40 weeks old specified pathogen f ree pigs and conventional pigs. A procedure to isolate lamina propria cells from porcine intestine was adapted for this study. The frequencies of IgM- , IgG-, and IgA-secreting (spot forming) cells were determined with a rever sed enzyme linked immunospot assay, which was also adapted for detection of Ig-SC in pigs. The Ig-SC frequencies were calculated as percentage of the mononuclear leukocytes isolated from the various organs. The observations t ill 40 weeks of age were as follows: Splenic IgM-SC predominated at all age s and reached a plateau of 0.1-0.2% of the mononuclear leukocytes already a t 4 weeks of age. The IgM-SC of mesenteric lymph node (MLN) predominated up till 12 weeks of age and reached an optimum of 0.15% reached at 4 weeks of age. The frequencies of IgG-SC of spleen and MLN had dips around 4 weeks o f age and increased thereafter till 40 weeks of age (spleen 0.025%, MLN 0.0 5% at 40 weeks of age). The frequencies of IgA-SC were low in the spleen (l ess than or equal to 0.003%) and moderate in the MLN (0.01-0.02%) at all ag es tested. In peripheral lymph node (PLN) and bone marrow (BM), the frequen cies of IgM-SC (0.03-0.05%) were much lower than in the spleen. The IgG-SC frequencies of BM and MLN also had dips around 4 weeks of age and increased thereafter. The IgG-SC frequency of BM reached a plateau at 12 weeks of ag e (0.15%) and for PLN the highest frequency was observed at 40 weeks of age (0.05%). The frequencies of IgA-SC were low in BM and PLN (< 0.003%). High frequencies of IgA-SC were observed in mucosa associated tissue like Peyer 's patches (PP) and intestinal lamina propria (till 20% of the mononuclear leukocytes in intestinal lamina propria of 12-40 weeks of age). IgM and IgA are both important isotypes in mucosal lymphoid organs in the pig. The shi ft from IgM to IgA as predominant, mucosal isotype was first observed in du odenum and jejunum (12 weeks) and later in ileum (40 weeks). The influence of ageing on the frequency of Ig-SC in PP was only observed in jejunal PP, whereas in ileal PP the frequencies of IQ-SC did not vary over time. We com bined our data about the frequencies of IgM-, IgG-, and IPI-SC in various o rgans with data obtained by others about the distribution of lymphocytes ov er porcine lymphoid organs at about 12 weeks of age. Based on these calcula tions we concluded that the small intestine, with more than 80% of all Ig-S C, is far most the major site of Ig production in the pig. We also conclude d that the small intestine is the major site of IgA and IgM production cell s in the pig. Although IgA becomes predominant along the intestine. the res ults demonstrated that in the pig IgM is more a mucosal isotype compared wi th other species. With 40% of all IgG-SC the porcine BM appeared to be the major site of IgG production. Unexpected results were obtained for IgG-SC i n the systemic lymphoid organs. In these organs the frequencies of IgG-SC d ropped firstly from 1 to 4 weeks of age and steadily increased thereafter t ill 40 weeks of age. This observation is discussed in relation to the possi bility that systemic IgG-SC at one week of age were passively acquired from maternal colostrum. The influence of housing/antigenic load at 10 weeks of age was mainly expre ssed by an increase (2 8x) of the frequency of IgG-SC in spleen, PLN, BM, a nd intestinal lamina propria, whereas the typical mucosal IgA-SC frequencie s in the lamina propria were hardly affected. (C) 1999 Elsevier Science Ltd . All rights reserved.