SummaryContinuous administration of soluble proteins, delivered over a 10-d period by a mini-osmotic pump implanted subcutaneously, induces a long-lasting inhibition of antigen-specific T cell prohferation in lymph node cells from BALB/c mice subsequently primed with antigen in adjuvant. The decreased T cell proliferative response is associated with a down-regulation of the T helper cell (Th)l cytokines interleukin (IL)-2 and interferon (IFN)-~/and with a strong increase in the secretion of the Th2 cytokines IL-4 and IL-5 by antigen-specific CD4 + T cells. This is accompanied by predominant inhibition of antigen-specific antibody production of IgG2a and IgG2b, rather than IgG1 isotype. Interestingly, inhibition of Thl and priming of Th2 cells is also induced in 132-microglobuhn-deficient BALB/c mice, indicating that neither CD8 + nor CD4 § NKI.1 + T cells, respectively, are required. The polarization in Th2 cells is stably maintained by T cell hnes, all composed ofCD4+/CD8 -cells expressing T cell receptor for antigen (TCR.)c~/I3 chains, derived from BALB/c mice treated with continuous antigen administration, indicating that they originate from Th2 cells fully differentiated in vivo. This polarization is induced in BALB/c mice by continuous administration of any protein antigen tested, including soluble extracts from pathogenic microorganisms. Priming of Th2 cells is dose dependent and it is optimal for low rather than high doses of protein. Blocking endogenous IL-4 in vivo inhibits expansion of antigen-specific Th2 cells, but does not restore IFN-~/production by T cells from mice treated with soluble antigen, indicating the involvement of two independent mechanisms. Consistent with this, Th2 cell development, but not inhibition of Thl cells, depends on non-major histocompatibility complex genetic predisposition, since the Th2 response is amphfied in BALB/c as compared to DBA/2, C3H, or C57BL/6 mice whereas inhibition of the Thl response is induced by soluble protein administration in any mouse strain tested. These findings support the hypothesis that continuous release of low amounts of protein antigens from pathogenic microorganisms may polarize the immune response toward a Th2 phenotype in susceptible mouse strains.

Differentiated T cells produce a restricted set of lymphokines, allowing their subdivision into two major subsets: Th1 and Th2 cells. This has lead to a new paradigm for immunoregulation based on the Th1/Th2 dichotomy. A strict compartmentalization of T cells into Th1 and Th2 is clearly an oversimplification: regulatory and effector mechanisms in the immune system encompass much more than Th1 and Th2 cells. This oversimplification is nevertheless useful to carry out experiments designed to test the paradigm. Based on results obtained in different experimental models of autoimmune diseases, the subdivision of T cells into Th1 and Th2 subsets has been extended to suggest that Th1 cells contribute to the pathogenesis of several organ-specific autoimmune diseases, whereas Th2 cells may inhibit disease development. Although more slowly and maybe less clearly, a similar dichotomy is starting to emerge in human autoimmune diseases. It will soon be possible to formally test immunointervention based on Th1/Th2 cell manipulation in clinical situations: the tools and a conceptual frame are already available. In this review we will examine two key factors affecting the Th1/Th2 balance: antigen and the role of cytokines influencing the development of Th1 and Th2 cells. The rational manipulation of these two variables may ultimately lead to an effective control of Th1 and Th2 cells potentially able to alter the natural course of human autoimmune diseases.

SummaryAntigen-presenting cells (APC) transfected with a construct encoding the hen egg-white lysozyme (HEL) amino acid sequence 1-80 constitutively present HEL peptides complexed to major histocompatibility complex (MHC) class II molecules to specific T cell hybridomas, indicating that endogenous cellular antigens can be efficiently presented to class II-restricted T cells. Here we show that exogenous peptide competitors added to HEL-transfected APC can inhibit the presentation of endogenous HEL peptides to class II-restricted T cells. The inhibition is specific for the class II molecule binding the competitor peptide, and it affects to the same extent presentation of exogenous or endogenous HEL peptides. These results, demonstrating that an exogenous competitor can inhibit class II-restricted T cell activation induced by endogenous as well as exogenous antigen, suggest lack of strict compartmentalization between endogenous and exogenous pathways of antigen presentation. Since autoreactive T cells may recognize endogenous, as well as exogenous antigens, the results have implications for the treatment of autoimmune diseases by MHC blockade.T cells recognize antigen as peptides bound to MHCencoded molecules on the surface of APC (1). Two classes of MHC molecules are involved in antigen presentation to T cells: class I molecules, expressed on the surface of the majority of nucleated cells (2), and class II molecules, expressed mainly on B cells, macrophages, and dendritic cells (3). Although class I and class II MHC molecules appear to have similar antigen-binding sites (4), they are loaded with peptides at different intracellular locations (5-8) and interact with different T cell populations, CD8 + or CD4 +, respectively (9). Two separate pathways of antigen processing and presentation have been proposed, leading to selective association of peptides from endogenous cellular antigens to class I molecules and of peptides from exogenous protein antigens to class II MHC molecules (10). However, peptides derived from endogenous cellular antigens can bind to class II molecules and be presented to T cells (11)(12)(13)(14).Here we demonstrate inhibition by an exogenous MHCbinding competitor of class II-restricted T cell activation induced by endogenously derived antigenic peptides, suggesting lack of strict compartmentalization between the two pathways. These results imply that administration of exogenous class II blockers may also inhibit presentation of endogenous antigens, including those potentially able to activate class II-restricted autoreactive T cells leading to MHC-linked autoimmune diseases. Materials and MethodsAntigens. The synthesis, purification, and analysis of HEL peptides have been previously described (15).Cell Cultures. The establishment of class II-restricted, HEL specific T cell hybridomas has been described (15). Cultures containing 5 x 104 T hybridoma cells and the indicated number of APC were set up in microtiter plates with or without antigen in 0.2 ml of RPMI 1640 (Gibco Laboratories, Grand Isl...

Mercury-induced autoimmune glomerulonephritis in the Brown-Norway (BN) rat is characterized by the successive appearance of linear and granular glomerular IgG deposits. Anti-laminin autoantibodies represent the major part of the anti-glomerular basement membrane (GBM) antibodies produced in this model. Fusions were performed in this model and four anti-GBM monoclonal antibodies (mAb) were obtained. Three of them were laminin specific. Using rabbit anti-idiotype antibodies, cross-reactive idiotypes (CRId) were characterized on anti-laminin antibodies. They were expressed on the three anti-laminin mAb, on kidney-eluted and circulating anti-laminin antibodies. CRId-bearing immunoglobulins were detected transiently in the circulation and paralleled the anti-laminin antibody activity. By immunofluorescence studies on kidney cryostat sections two different CRId were defined. One was localized close to the antigen-combining site since it was not revealed on kidney-bound antibodies, in contrast with the second CRId. This latter CRId was also found deposited in a typical linear pattern in the early phase of the disease and in a granular pattern in the late phase, demonstrating that these CRId are components of immune deposits. Taken together, these results suggest that in this model of T-dependent polyclonal B cell activation, restricted sets of V genes encode for at least a part of the anti-GBM autoantibodies.