Microbial induction of B and T cell areas in rabbit appendix

Gut-associated lymphoid tissue (GALT) development requires interaction with the intestinal microbiota. Because murine secondary lymphoid tissue development is driven by positive feedback interactions between B cells and stromal cells, we used in situ hybridization to determine whether intestinal commensals influence such interactions during rabbit appendix development. The features of positive feedback interactions we examined (CXCL13 mRNA expression, B cell accumulation and FDC differentiation) increased during early follicle development, but stalled in the absence of intestinal commensals. These features were reinitiated by commensals that stimulated follicle development and intrafollicular B cell proliferation. Our results suggest that rabbit appendix follicles develop in two phases: an initial phase of B cell recruitment to nascent follicles, possibly through positive feedback interactions, and a subsequent phase of intrafollicular B cell proliferation stimulated by intestinal commensals. In addition, we found that intestinal commensals stimulate appendix CCL21 mRNA expression and T cell area formation.

Temporal development of B and T cell areas in the neonatal rabbit appendix. (90.14)

The rabbit appendix is organized structurally into multiple B cell follicles separated, at their sub-apical regions, by well-defined T cell areas. We found, by RNA in situ hybridization, that the B cell chemoattractant CXCL13 (B-lymphocyte chemoattractant, or BLC) is highly expressed in the B cell follicles. In addition, we found that the T cell chemoattractant CCL21 (secondary lymphoid tissue chemokine, or SLC) is highly expressed in the T cell areas. The localized expression of these chemoattractants likely organizes the B and T cell areas of the appendix. Surprisingly, however, we found that the localized expression of CXCL13 and CCL21 differs dramatically in early neonatal appendix. At two days after birth, CXCL13 expression was confined to the appendix domes and CCL21 expression was localized in a continuous layer significantly beneath the domes. Over subsequent days, as B cells accumulated in the domes and began proliferating, developing follicles gradually distended downward through the layer of CCL21 expression, ultimately generating the characteristic organization of B and T cell areas seen in the adult appendix. This developmental process might be important in establishing an environment supportive of B cell proliferation and antibody repertoire diversification, which occur in the rabbit appendix between 3 and 6 weeks of age.

Topical PDGF-BB results in limited healing in a patient with Werner's syndrome and chronic leg ulcers

Impaired wound healing is a feature of Werner's syndrome. Treatment of one such patient with painful chronic leg ulcers included topical application of PDGF-BB. Granulation increased slightly, enabling full-thickness skin grafting to take place.