Major histocomatibility complex (MHC) class II molecules are required for the normal development in the thymus of CD4+ T cells and function to present peptide antigens to those CD4 cells in the periphery.
The distribution of class II molecules is limited to thymic epithelial cells-where they are required for the positive and negative selection of CD4+ T cells-and in the periphery where they are required for the survival and activation of those T cells. We have developed a series of transgenic mice with restricted expression of the MHC class II molecule, I-Ab, and used them to investigate the requirement for different populations of antigen presenting cells in the thymic selection, peripheral activation, and tolerance of CD4+ T cells. Our most well studied model is the K14 mouse in which MHC molecules are restricted to thymic cortical epithelium-both thymic medullary epithelium and bone marrow-derived cells are class II negative. Positive selection of CD4+ T cells does occur in the K14 thymus; however, clonal deletion of autoreactive thymocytes can not be detected. Thus, K14 CD4 cells proliferate to I-Ab-positive APC in vitro and cause graft-versus-host disease when injected into MHC-identical hosts. Our current studies are directed toward understanding the peptide specificity, function, and pathologic potential of these autoreactive T cells:
1) Examination of a series of K14-derived autoreactive T hybridomas demonstrates that the autoreactive population of CD4 cells is polyclonal; however, we are beginning to identify the individual peptides responsible for stimulating the autoreactive response. To better understand the thymic selection processes in both K14 and wildtype thymi, we have also derived TCR transgenics from two of the hybrids and have begun to analyze the thymic development and peripheral function of autoreactive TCR transgenic CD4+ T cells in both K14 and wildtype mice of various haplotypes, including NOD, the diabetogenic genotype.
2) Development of autoimmunity: Adoptive transfer systems are being utilized to tease apart the T cell and target-organ abnormalities that must be present to initiate an autoimmune disease. Disease models include graft-versus-host disease, Herpes simplex keratitis, and Type I diabetes.
3) Requirement for MHC class II in other antigen presenting populations. Our newest transgenics utilize the mb-1 and CD11c promoters to reexpress class II molecules in the B cells and dendritic cells, respectively, of class II-deficient mice. Studies will be directed towards understanding how limiting the expression of Class II molecules alters the positive and negative selection, peripheral survival, and peripheral survival and effector function of CD4+ T cells.
Gene repair construct. Mouse is MHCII-negative unless crossed to a Cre. Cre expression drives MHCII expression.
MHCII restricted to CD19+ B cells.
MHCII expression restricted to conventional DCs. Normal levels in CD8a+ DCs. Slightly reduced in CD11b+ DCs in spleen. pDCs MHCII negative. Langerhans cells MHCII negative and dermal DCs with very low levels of MHCII. NO CD4+ T cells.
CreT2 driven off human CD20 BAC. After Tamoxifen, Cre is expressed in 75-95% of splenic B cells. Expression initiates quite late in BM.
MHC class II expression restricted to thymic cortical epithelium. CD4+ conventional and Tregs positively selected by no MHCII interation in thymic medulla or periphery
Same source as Abb-/- sold by Taconic, originally made by Laurie Glimcher.
GFP driven off a RAG BAC. Marks RAG expression. Additionally, GFP persists longer than RAG and so marks recent thymic emigrants.