Mice deficient in lymphotoxin β receptor (LTβR) or interleukin 7 receptor α (IL-7Rα) lack Peyer's patches (PPs). Deficiency in CXC chemokine receptor 5 (CXCR5) also severely affects the development of PPs. A molecular network involving these three signaling pathways has been implicated in PP organogenesis, but it remains unclear how they are connected during this process. We have shown that PP organogenesis is initiated at sites containing IL-7Rα+ lymphoid cells and vascular cell adhesion molecule (VCAM)-1/intercellular adhesion molecule (ICAM)-1 expressing nonlymphoid elements. Here we characterize these lymphoid and nonlymphoid components in terms of chemokine signals. The lymphoid population expresses CXCR5 and has a strong chemotactic response to B lymphocyte chemoattractant (BLC). Importantly, chemokines produced by VCAM-1+ICAM-1+ nonlymphoid cells mediate the recruitment of lymphoid cells. Furthermore, we show that these VCAM-1+ICAM-1+ cells are mesenchymal cells that are activated by lymphoid cells through the LTβR to express adhesion molecules and chemokines. Thus, promotion of PP development relies on mutual interaction between mesenchymal and lymphoid cells.

A rat Ia (RT-1B) antigen (called Ia-A) equivalent to the mouse I-A product has been defined with mouse monoclonal antibodies (W. R. McMaster and A. F. Williams, Eur. J. Immunol. 1979. 9: 426). To identify other Ia antigens mouse monoclonal antibodies were raised against rat spleen glycoproteins depleted of the Ia-A antigen. An IgG antibody (called MRC OX17) was obtained and used to purify a molecule which had a similar structure to the Ia-A antigen and reacted with anti-Ia alloantibodies. There was no cross-reaction between the two Ia glycoproteins in assays with mouse monoclonal antibodies, alloantibodies or rabbit antibodies. In one alloantiserum almost all the detectable anti-Ia antibodies reacted with a mixture of the two Ia glycoproteins. The MRC OX17 antibody did not bind to mouse cells, but rabbit antibodies to the pure rat glycoprotein cross-reacted and recognized determinants mapping to the mouse I-E region. In the thymus the rat Ia-E antigen was on cortical epithelial and medullary reticular cells. An IgG monoclonal antibody (MRC OX18) to isotypic determinants of rat histocompatibility RT-1A antigens was also produced and used to analyze these antigens on thymus cells. The heavily labeled thymocytes were those with characteristics of mature T lymphocytes. Cortical epithelial cells and medullary dendritic-like cells were also RT-1A positive.

It is suggested that Langerhans cells and CD8-positive T cell may play a major role in the pathogenesis of the oral lichenoid lesions of cGVHD, and the immune response was inducted in OLP as well as the oral lichenoid lesion of cGVHD in this study.

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