Antibody Repertoire Development in Fetal and Neonatal Piglets. XX. B Cell Lymphogenesis Is Absent in the Ileal Peyer’s Patches, Their Repertoire Development Is Antigen Dependent, and They Are Not Required for B Cell Maintenance

Abstract

The continuous ileal Peyer’s patches (IPP) of sheep are regarded as a type of mammalian bursal equivalent where B cells diversify their repertoire in an Ag-independent fashion. Anatomically and developmentally similar IPP occur in swine. Resection of ∼90% of the IPP in piglets at birth did not alter Ig levels in serum and secretions or retard diversification of the Ab repertoire when animals were maintained in isolators and colonized with a defined gut flora. Resection or sham surgery elevated IgG and IgA in serum and in lavage fluid from the gut, lung, and in saliva. No changes in the frequency of IgG-, IgA-, and IgM-containing cells in the spleen and peripheral lymph node were observed. Using an index that quantifies diversification of the VDJ repertoire, no differences were seen in three secondary lymphoid tissues between piglets lacking IPP and colonized controls, whereas both groups displayed >10-fold greater diversification than did late-term fetal piglets or piglets maintained germ-free. Somatic hypermutation was very low in fetal IPP and the IPP of germ-free piglets but increased 3- to 5-fold after colonization. D–J signal joint circles were not recovered in IPP, and V–DJ signal joint circles were 5-fold lower than in bone marrow and similar to those in thymus and spleen. We conclude that the porcine IPP are not a site of B cell lymphogenesis, do not undergo Ag-independent repertoire diversification, and are not primary lymphoid tissue since they are not required for maintenance of Ig levels in serum and secretions.

Ileal Peyer’s Patches Are Not Necessary for Systemic B Cell Development and Maintenance and Do Not Contribute Significantly to the Overall B Cell Pool in Swine

“…These investigators found that resection of the sheep IPP resulted in a prolonged B cell deficiency, although this deficiency did not alter serum Ig levels (49). The latter is consistent with our findings (39). It is possible that this discrepancy could be methodological since evidence for B cell deficiency in lambs with resected IPP was based on manual counting of limited numbers of Ig + B cells using a slide smear method (17) that can generate a significant error.…”

“…The shift from the fetal to the adult type of lymphocyte distribution and its dependence on degree of colonization indicate that events in the IPP proceed in an Ag-dependent manner, as in secondary lymphoid tissues. This conclusion is supported by findings that the shift is also accompanied by an increase in Ab repertoire diversification (39) (Fig. 2), which also characterize secondary lymphoid tissues (31,33,34).…”

“…After birth, piglets were kept in isolator units under germ-free conditions at all times and were maintained on a diet of Esbilac (PetAg, Hamilton, IA), which was adjusted daily to meet their daily nutrient requirements and to maintain adequate caloric intake. Piglets designed for surgery treatment were operated ∼48 h after birth (total of 16 animals) as described elsewhere (38,39), whereas other piglets were left untreated (total of 11 animals). Surgical treatment involved 1) a group of piglets with surgically removed IPP (total of eight animals), 2) a group of piglets with surgically constructed isolated ileal loop and simultaneously anastomosed (rejoined) the rest of ileum (total of three animals), or 3) group of sham operated piglets with a transected and thereafter anastomosed lower ileum (total of five animals).…”

B Cell Lymphogenesis in Swine Is Located in the Bone Marrow

“…However, pigs, together with all other ungulates, were speculated for .30 y to belong to species that use ileal Peyer's patches for development of B cells (10,11,25). We have previously shown that ileal Peyer's patches are not required for B cell development and maintenance (12)(13)(14), and that this role has probably been filled by the BM (26)(27)(28)(29)(30). In the present study we have finally shown that B cell lymphogenesis in pigs clearly occurs in the BM.…”

“…These species use specialized GALTs located in a hindgut, and include gallinaceous birds that use the bursa of Fabricius, rabbits that use the sacculus rotundus, and ungulates, including swine, that use ilealthis categorization by showing that at least in swine (and probably in other ungulates), ileal Peyer's patches are not a significant source of B cells, are not required for maintenance of the systemic B cell pool, and are not a site of primary B cell lymphogenesis (12)(13)(14). The results of the present study extend those studies by showing that porcine B cells are developed throughout life in the BM, the primary lymphoid organ also for mice and humans (2,3).…”