Enhanced glial activation and expression of specific CNS inflammation-related molecules in aged versus young rats following cortical stab injury.

Aging is associated with increased glial responsiveness that may enhance the brain's susceptibility to injury and disease. To determine whether unique age-related molecular responses occur in brain injury, we assessed mRNA levels of representative central nervous system (CNS) inflammation-related molecules in young (3 months) and aged (36 months) Fisher 344/Brown Norwegian F1 hybrid rats following cortical stab. Enhanced glial activation in older animals was accompanied by increased expression of a subset of inflammation-related mRNAs, including IL-1beta, TNFalpha, IL-6, ICAM-1, inducible nitric oxide synthase (iNOS), metalloproteinase-9 (MMP-9), and complement 3alpha-chain 1 (C3alpha1). Recognition of these age-specific differences may guide development of novel treatment regimes for older individuals.

Models of inflammation: adjuvant-induced arthritis in the rat.

Injection of adjuvant (Mycobacterium butyricum suspended in mineral oil) into rats produces an immune reaction that characteristically involves inflammatory destruction of cartilage and bone of the distal joints with concomitant swelling of surrounding tissues. Adjuvant-induced arthritis in rats is commonly used to evaluate compounds that might be of potential use as drugs for treatment of rheumatoid arthritis and other chronic inflammatory conditions. This unit describes a method for inducing arthritis by injecting adjuvant into the tail and evaluating a test compound for the ability to inhibit the inflammatory response.

Role of APC in the selection of immunodominant T cell epitopes.

Following antigenic challenge, MHC-restricted T cell responses are directed against a few dominant antigenic epitopes. Here, evidence is provided demonstrating the importance of APC in modulating the hierarchy of MHC class II-restricted T cell responses. Biochemical analysis of class II:peptide complexes in B cells revealed the presentation of a hierarchy of peptides derived from the Ig self Ag. Functional studies of kappa peptide:class II complexes from these cells indicated that nearly 20-fold more of an immunodominant epitope derived from kappa L chains was bound to class II DR4 compared with a subdominant epitope from this same Ag. In vivo, T cell responses were preferentially directed against the dominant kappa epitope as shown using Ig-primed DR4 transgenic mice. The bias in kappa epitope presentation was not linked to differences in class II:kappa peptide-binding affinity or epitope editing by HLA-DM. Rather, changes in native Ag structure were found to disrupt presentation of the immunodominant but not the subdominant kappa epitope; Ag refolding restored kappa epitope presentation. Thus, Ag tertiary conformation along with processing reactions within APC contribute to the selective presentation of a hierarchy of epitopes by MHC class II molecules.

Presentation of abundant endogenous class II DR-restricted antigens by DM-negative B cell lines.

Peptides derived from endogenous and exogenous antigens compete for binding and presentation via class II molecules. Studies with mutant B cell lines defective in exogenous antigen presentation suggest that HLA-DM molecules facilitate the interaction of foreign peptides and class II molecules. In contrast, presentation of self antigens is not strictly dependent upon HLA-DM, as demonstrated by the ability of these mutant cells to activate T cells specific for endogenous antigens. Two distinct classes of DM-negative cells, T2 cells generated by in vitro mutagenesis and lines derived from bare lymphocyte syndrome (BLS) patients, were able to present epitopes derived from self proteins. Transfection of DM genes into the mutant cells enhanced the presentation of some, but not all, endogenous antigens, suggesting that formation of select endogenous peptide/class II complexes is not dependent upon DM. The efficiency of endogenous antigen presentation in the absence of DM was also dependent on the mutant antigen-presenting cell studied, as the TxB hybrid T2 presented greater amounts of self peptides compared to cells from BLS patients. Thus, additional genes, aside from DM, may regulate the pathway for endogenous antigen presentation.

Coordinate defects in human histocompatibility leukocyte antigen class II expression and antigen presentation in bare lymphocyte syndrome.

The human immunodeficiency, type II bare lymphocyte syndrome (BLS), has been attributed to a defect in the transcription of class II histocompatibility genes. Immunocompetence, as assessed by functional exogenous antigen presentation, was not restored in immortalized B cells, derived from a BLS patient, after transfection with HLA-DR class II structural genes. Incubation of protein antigens, as well as infectious virus, with DR-transfected BLS cells failed to induce activation of antigen-specific helper T lymphocytes. Peptide antigens were presented by class II molecules displayed on BLS cells, although the conformation of these class II proteins was altered as indicated by epitope mapping. This defect in antigen presentation was independent of the specific class II DR allele transfected into BLS cells. Genetic complementation analysis has been used with BLS cells to demonstrate that the defect in class II gene transcription is linked to the absence of a trans-acting factor. Similarly, functional class II dimers were restored after in vitro fusion of cells derived from two distinct BLS complementation groups, implying that specific transcriptional control elements are shared by a gene critical for antigen presentation and genes encoding HLA class II antigens. Thus, two important functionally linked pathways of class II molecules, structural gene expression and antigen presentation, share a common regulatory pathway defective in BLS.