Figure 4Cross-reactivity of GA-reactive T-cell lines is increased after daily injections of GA. Percentages of the GA-induced T-cell lines cross-reacting to each APL tested at each time point are shown for the 7 patients encoded by gray scale. Proliferative IFN-γ and IL-5 responses were examined for all T-cell lines and are represented separately in the top, middle, and lower third. A minimum SI of 2 and a difference of 2 SD over the background was required for classification as a cross-reactive T-cell line.

Traditionally, emphasis has been placed on the roles of Th cells in generating and amplifying both cellular and humoral memory responses. Little is known about the potential contributions of B cell subsets to immunological memory. Resting memory B cells have generally been regarded as poor APC, attributed in part to the relative paucity of costimulatory molecules identified on their surface. We describe a novel subpopulation of human memory B cells that express CD80 in their resting state, are poised to secrete particularly large amounts of class switched Igs, and can efficiently present Ag to and activate T cells. This functionally distinct B cell subset may represent an important mechanism by which quiescent human B cells can initiate and propagate rapid and vigorous immune memory responses. Finally, these studies extend recent observations in the murine system and highlight the phenotypic and functional diversity that exists within the human B cell memory compartment.

The capacity of glatiramer acetate (GA), a random copolymer of alanine, lysine, glutamic acid, and tyrosine to stimulate primary in vitro human and murine T cell proliferation was examined. PBMCs isolated from healthy humans and relapsing remitting multiple sclerosis patients and spleen cells from inbred strains of mice, expressing different H-2 haplotypes, were used as sources of non-GA-primed lymphocytes. GA functioned as a universal Ag, inducing dose-dependent proliferation of all non-GA-primed human and murine T cell populations tested. Moreover, GA stimulated PBMCs derived ex vivo from human cord blood, strongly suggesting that GA can activate both naive and memory T cells. The human T cell proliferative responses to GA were HLA class II DR-restricted by virtue of the ability of anti-class II Ab to inhibit T cell proliferation, and the demonstration that individual GA specific human T cell clones were HLA class II DR-restricted by either restriction element but not both. Furthermore, GA-reactive T cells secreted Th0 cytokines and expressed a diverse repertoire of TCR. Limiting dilution analysis indicated that the T cell precursor frequency among the healthy human adults tested ranged from 1:5,000 to 1:125,000. Given that all of the T cell populations tested were isolated from non-GA-primed donors, it appears that virtually all humans and murine strains contain significant numbers of T cell populations cross-reactive with GA. These findings may explain the recent clinical finding that daily s.c. administration of GA ameliorates the progression of multiple sclerosis.

Malignant gliomas (MGs), lethal human central nervous system (CNS) neoplasms, contain tumor infiltrating lymphocytes (TIL). Although MHC class II molecules are frequently detected on MG cells, suggesting that they may be capable of antigen (Ag) presentation to CD4(+) T cells, deficiencies in CD4(+) T-cell activation are associated with these nonimmunogenic tumors. We evaluated regulation of the MHC class II transactivator (CIITA), the key intermediate that controls class II expression, in MG cells and tested whether MG cells could process native Ag. After interferon-gamma (IFN-gamma) stimulation, MG cells upregulated CIITA and class II molecules. IFN-gamma-inducible CIITA expression in MG cells, as well as primary human astrocytes, was directed by two CIITA promoters, pIV, the promoter for IFN-gamma-inducible CIITA expression in nonprofessional antigen-presenting cells (APC), and pIII, the promoter that directs constitutive CIITA expression in B cells. Both pIII and pIV directed CIITA transcription in vivo in MGs and ex vivo in IFN-gamma-activated primary MG cultures. We also demonstrate for the first time that MG cells can process native Ag for presentation to CD4(+) MHC class II-restricted Th1 cells, indicating that MG cells can serve as nonprofessional APC. CIITA may be a key target to modulate MHC class II expression, which could augment immunogenicity, Ag presentation, and CD4(+) T-cell activation in MG therapy.

No abstract

Since the mechanism of T cell inhibition by RCs appears to be different than that of rapamycin (RAP) or cyclosporin A (CsA), they may provide a new tool to investigate intracellular signaling in T cells, and may present novel opportunities for immunosuppression

No abstract

The random amino acid copolymer poly(Y,E,A,K)n (Copaxone®) is widely used in multiple sclerosis treatment and a second generation copolymer poly(Y,F,A,K)n with enhanced efficacy in experimental autoimmune encephalomyelitis in mice has been described. A major mechanism through which copolymers function to ameliorate disease is the generation of immunosuppressive IL-10-secreting regulatory T cells entering the CNS. In addition, the antigen presenting cell to which these copolymers bind through MHC Class II proteins may have an important role. Here, both CCL22 (a Th2 cell chemoattractant) in large amounts and CXCL13 in much smaller amounts are shown to be secreted after administration of YFAK to mice and to a smaller extent by YEAK parallel to their serum concentrations. Moreover, bone marrow-derived macrophages secrete CCL22 in vitro in response to YFAK and to higher concentrations of YEAK. Strikingly, these chemokines are also secreted into serum of MHC Class II −/− mice, indicating that an innate immune receptor on these cells also has an important role. Thus, both the innate and the adaptive immune systems are involved in the mechanism of EAE amelioration by YFAK. The enhanced ability of YFAK to stimulate the innate immune system may account for its enhanced efficacy in EAE treatment.