Interference with CD28, CD80, CD86 or CD152 in collagen-induced arthritis. Limited role of IFN-gamma in anti-B7-mediated suppression of disease

We have investigated interference with co-stimulation by administering mAbs towards CD28, CD80, CD86, and CD152 in mice immunized for the development of collagen-induced arthritis (CIA). Anti-CD80 and anti-CD86 treatment inhibited disease score and incidence, whereas anti-CD28 treatment led only to a delayed disease onset. Administration of anti-CD152 had no effect. The CII-specific Ab-response was suppressed by the co-stimulatory blockade, with a stronger effect on IgG1 than on IgG2a. The CII-driven T cell proliferation, on the other hand, was not affected. Furthermore, T cells primed in the presence of either anti-B7 or anti-CD28 produced markedly increased amounts of IFN-gamma in response to CII. To investigate whether this increase in IFN-gamma was related to disease suppression, IFN-gamma-deficient mice were immunized with CII, treated with anti-B7 and followed for the development of arthritis. As in the wild-type mice, administration of anti-B7 to IFN-gamma-deficient mice led to a reduced disease incidence and severity as well as reduced anti-CII IgG titers. Collectively, these data stress the importance of co-stimulation for the delivery of B cell help rather than for production of Th1 cytokines. We also demonstrate that the enhanced production of IFN-gamma observed after B7-blockade is not accountable for the anti-B7 mediated inhibition of CIA.

Potent adjuvant effect by anti-CD40 in collagen-induced arthritis. Enhanced disease is accompanied by increased production of collagen type-II reactive IgG2a and IFN-gamma

Collagen type II-induced arthritis (CIA) is an experimental model of rheumatoid arthritis, an autoimmune inflammatory disease of the peripheral joints in humans. CD40 interaction with its ligand CD154 (CD40L) has been shown to be an obligatory step in the initiation of autoimmune disease in several animal models. In this study we report on the effect of CD40 stimulation in CIA induced by immunization with type II collagen (CII) in CFA or IFA. We found that the administration of stimulatory anti-CD40 mAb resulted in earlier onset and more severe disease in IFA-CII-immunized mice. The mAb treatment resulted in markedly elevated titers of CII-specific IgG2a antibodies whereas CII-specific IgG1 titers were unaffected. Draining lymph node cell cultures from mice treated with anti-CD40 exhibited significantly increased IFN-gamma production compared to cultures from control antibody-treated mice. In conclusion, our results indicate that the level of CD40 activation during the induction of an autoimmune response may determine the severity of the resulting disease.

CTLA-4 ligation suppresses CD28-induced NF-kappaB and AP-1 activity in mouse T cell blasts

The effects of cytotoxic lymphocyte antigen 4 (CTLA-4) on CD3/CD28 monoclonal antibody (mAb) activation of CD4(+)/CTLA-4(+) blastoid T cells were studied in an in vitro model system. As previously reported, coligation of CTLA-4 mAb results in suppression of T cell proliferation and cytokine production. The proliferation but not the interleukin 2 (IL-2) production could be restored by addition of exogenous IL-2, suggesting that the inhibitory effect occurred at the level of IL-2 production rather than at the regulation of the IL-2 receptor pathway. To study the effects on nuclear factors critical for T cell activation, we analyzed the levels of the transcription factors NF-kappaB and AP-1. These were potently induced in CD3/CD28 mAb-restimulated T cells. In contrast, CTLA-4 ligation strongly suppressed the induction of both transcription factors. The compositions of NF-kappaB and AP-1 family members were similar, irrespective of stimulation conditions. Analyses of the NF-kappaB regulator IkappaB-alpha revealed similar levels of IkappaB-alpha protein in the preparations. However, a reduced phosphorylation of IkappaB-alpha in CTLA-4 coengaged T cell blasts compared with T cells ligated with CD3/CD28 was found. Previous studies have concluded that CTLA-4 ligation regulates T cell activation by inhibiting the T cell receptor-mediated signals. However, the present findings propose that the major impact of CTLA-4 ligation is inhibition of signals mediated by CD28.

Epitope glycosylation plays a critical role for T cell recognition of type II collagen in collagen-induced arthritis

Immunization of mice with type II collagen (CII) leads to collagen-induced arthritis (CIA), a model for rheumatoid arthritis. T cell recognition of CII is believed to be a critical step in CIA development. We have analyzed the T cell determinants on CII and the TCR used for their recognition, using twenty-nine T cell hybridomas derived from C3H.Q and DBA/1 mice immunized with rat CII. All hybridomas were specific for the CII(256-270) segment. However, posttranslational modifications (hydroxylation and variable O-linked glycosylation) of the lysine at position 264 generated five T cell determinants that were specifically recognized by different T cell hybridoma subsets. TCR sequencing indicated that each of the five T cell epitopes selected its own TCR repertoire. The physiological relevance of this observation was shown by in vivo antibody-driven depletion of TCR Valpha2-positive T cells, which resulted in an inhibition of the T cell proliferative response in vitro towards the non-modified CII(256-270), but not towards the glycosylated epitope. Most hybridomas (20/29) specifically recognized CII(256-270) glycosylated with a monosaccharide (beta-D-galactopyranose). We conclude that this glycopeptide is immunodominant in CIA and that posttranslational modifications of CII create new T cell determinants that generate a diverse TCR repertoire.

Receptor for alpha1-microglobulin on T lymphocytes: inhibition of antigen-induced interleukin-2 production

The human plasma protein alpha1-microglobulin (alpha1m) was found to inhibit the antigen-induced interleukin-2 (IL-2) production of two different mouse T-helper cell hybridomas. Alpha1m isolated from human plasma and recombinant alpha1m isolated from baculovirus-infected insect cell cultures had similar inhibitory effects. Flow cytometric analysis showed a binding of plasma and recombinant alpha1m to the T-cell hybridomas as well as to a human T-cell line. Radiolabelled plasma and recombinant alpha1m bound to the T-cell hybridomas in a saturable manner and the binding could be eliminated by trypsination of the cells. The affinity constants for the cell binding were calculated to be 0.4-1 x 10(5) M(-1) using Scatchard plotting, and the number of binding sites per cell was estimated to be 5 x 10(5)-1 x 10(6). The cell-surface proteins of one of the T-cell hybridomas were radiolabelled, the cells lysed and alpha1m-binding proteins isolated by affinity chromatography. SDS-PAGE and autoradiography analysis of the eluate revealed major bands with Mr-values around 70, 35 and 15 kDa. The results thus suggest that alpha1m binds to a specific receptor on T cells and that the binding leads to inhibition of antigen-stimulated IL-2 production by T-helper cells.

Biased dependency of CD80 versus CD86 in the induction of transcription factors regulating the human IL-2 promoter

In addition to the signals obtained by ligation of the TCR, T cells need additional, co-stimulatory signals to be activated. One such co-stimulatory signal is delivered when CD28 on T cells binds to CD80 or CD86 on antigen-presenting cells (APC). In the present study, we analyzed the ability of CD80 and CD86 to co-stimulate human T cells activated by superantigen. Using the Raji B cell lymphoma, which express similar levels of CD80 and CD86, it was found that T cell proliferation was mainly co-stimulated by CD80. To further characterize the consequences of this biased co-stimulatory dependency, we employed a well-defined system of transfected CHO cells expressing human MHC class II together with CD80, CD86 or CD80 and CD86. Proliferation of freshly prepared CD4+ T cells required the presence of either CD80 or CD86. However, IL-2 production reached only suboptimal levels in the presence of CD86 but optimal levels with CD80. To analyze IL-2 transcriptional activity in CD80 and CD86 co-stimulated T cells we used Jurkat T cells transfected with luciferase reporter gene constructs. CD80 induced higher levels of IL-2 promoter-enhancer activity compared to CD86. Furthermore, the activity of transcription factors regulating the IL-2 promoter-enhancer region including activation protein-1, CD28 response element and nuclear factor kappaB were 4-8 times higher after CD80 compared to CD86 ligation. Our results suggest that the eventual appearance of CD80 on recently activated CD86+ APC is important for the superinduction of IL-2 production and to support vigorous T cell proliferation.

Antigen processing and presentation of a naturally glycosylated protein elicits major histocompatibility complex class II-restricted, carbohydrate-specific T cells

It is well known that T cells recognize antigen as processed peptides bound to major histocompatibility complex molecules on the surface of antigen-presenting cells. Recently, it has been shown that T cells can specifically recognize synthetic glycopeptides. However, whether glycopeptides are selected for presentation during antigen processing of glycoproteins and eventually elicit carbohydrate-specific T cells is still an open question. In this study, we utilized synthetic glycopeptides to analyze T cell recognition of the naturally glycosylated immunodominant peptide representing type II collagen (CII) residues 256-270. In this peptide, lysines at positions 264 and 270 may be post-translationally modified by hydroxylation and subsequent O-linked glycosylation with beta-galactosyl or alpha-glucosyl-(1-->2)-beta-galactosyl residues. T cell hybridomas established from type II collagen-immunized mice specifically recognized CII 256-270 with either galactose or glucosyl-galactose at position 264. The T cell hybridoma recognizing glucosyl-galactose displayed no cross-reactivity either to galactose or to the structurally different alpha-galactosyl-(1-->4)-beta-galactose. Furthermore, the T cell hybridoma recognizing galactose did not cross-react to glucosyl-galactose or galactosyl-galactose, indicating that the antigen-presenting cells (bulk spleen cells, lipopolysaccharide-stimulated spleen cells, anti-CD40-stimulated spleen cells, peritoneal exudate cells or CFA-primed lymph node cells) inefficiently processed carbohydrates when the antigen was given as a glycopeptide.

Systemic versus cartilage-specific expression of a type II collagen-specific T-cell epitope determines the level of tolerance and susceptibility to arthritis

Immunization of mice with rat type II collagen (CII), a cartilage-specific protein, leads to development of collagen-induced arthritis (CIA), a model for rheumatoid arthritis. To define the interaction between the immune system and cartilage, we produced two sets of transgenic mice. In the first we point mutated the mouse CII gene to express an earlier defined T-cell epitope, CII-(256-270), present in rat CII. In the second we mutated the mouse type I collagen gene to express the same T-cell epitope. The mice with mutated type I collagen showed no T-cell reactivity to rat CII and were resistant to CIA. Thus, the CII-(256-270) epitope is immunodominant and critical for development of CIA. In contrast, the mice with mutated CII had an intact B-cell response and had T cells which could produce gamma interferon, but not proliferate, in response to CII. They developed CIA, albeit with a reduced incidence. Thus, we conclude that T cells recognize CII derived from endogenous cartilage and are partially tolerized but may still be capable of mediating CIA.

Macrophages, but not dendritic cells, present collagen to T cells

Dendritic cells, such as epidermal Langerhans cells, play a crucial role for the antigen-specific priming of T cells. We have addressed the question whether dendritic cells present collagen, a major protein component in tissues through which dendritic cells migrate, i.e. the basement membrane, dermis, and synovial tissue. Langerhans cells, spleen cells and peritoneal macrophages were compared for antigen-presenting capacity using a panel of mouse T cell hybridomas reactive with different determinants on type II collagen, myelin basic protein, ovalbumin and pepsin. Langerhans cells did not present any of the type II collagen determinants, unless the antigen was administered as a 15-mer peptide, but did present myelin basic protein, ovalbumin and pepsin. Spleen cells and peritoneal macrophages, in contrast, presented all type II collagen determinants. This biased antigen presentation was also observed when Langerhans cells were pulsed with antigen in vivo. The inability to present type II collagen is related to the collagen sequence as such, since both native type II collagen, type II collagen alpha chains, as well as a type II collagen determinant incorporated in type I collagen, were not presented by Langerhans cells. In addition, granulocyte/macrophage colony-stimulating factor-expanded blood dendritic cells displayed the same biased antigen presentation, suggesting that the inability to present collagen is not restricted to dendritic cells localized in epidermis. B cell-deficient mice could prime a type II collagen-reactive T cell response, thus excluding B cells as obligatory antigen-presenting cells for the priming of collagen-reactive T cells. We suggest that neither Langerhans cells nor B cells, but macrophages are the primary antigen-presenting cells in the immune response towards type II collagen.

T cell recognition of carbohydrates on type II collagen

A critical event in an immune response is the T cell recognition of peptides bound to major histocompatibility complex (MHC) molecules on the surface of an antigen presenting cell (APC). Although the majority of eukaryotic proteins are glycosylated, it has not yet been shown that T cell recognition of such proteins involves recognition of the bound carbohydrates. Type II collagen (CII), the major protein constituent of joint cartilage, is posttranslationally modified by hydroxylation and glycosylation of lysines. In this report we show that posttranslational modifications of the immunodominant peptide CII(256-270) generate a structural determinant that is distinct from the determinant represented by the corresponding synthetic peptide. Elimination of carbohydrates, present on CII, by two different biochemical methods revealed that the carbohydrates, O-linked to the hydroxylysines within the CII(256-270) determinant, were crucial for the reactivity towards the posttranslationally modified peptide. Furthermore, a T cell hybridoma specific for the glycosylated determinant was stimulated by tryptic CII-peptides presented by fixed APCs, thus showing that the carbohydrates are involved in the trimolecular complex T cell receptor/peptide/MHC. Finally, the importance of the bound carbohydrates for the arthritogenicity of CII was investigated by comparing the development of arthritis after immunization with carbohydrate-depleted and glycosylated CII, respectively. Incidence, time of onset, and severity of the disease were significantly affected by the elimination of carbohydrates, whereas no significant difference in anti-CII antibody titers was seen.

Expression of a transgenic class II Ab gene confers susceptibility to collagen-induced arthritis

The major histocompatibility complex (MHC) class II region is assumed to influence autoimmune diseases such as rheumatoid arthritis. In the mouse, the H-2q haplotype is associated with susceptibility to collagen-induced arthritis, while the H-2p haplotype is not. The class II A molecules of these haplotypes differ by only four amino acids in the first domain of the beta chain. To test if this difference accounts for the MHC influence on susceptibility to collagen-induced arthritis, H-2p mice were made transgenic with an Abp gene altered to resemble the Abq gene. The transgenic A beta chain hybridized with the A alpha p chain and was shown to be physiologically expressed by testing antigen-presentation capacity to Aq-restricted T cell hybridomas and with FACS analyses. These transgenic mice developed an autoimmune response to type II collagen and also collagen-induced arthritis. The data unequivocally suggest the Ab gene as a major genetic susceptibility locus for autoimmune collagen-induced arthritis.

Identification of an immunodominant type-II collagen peptide recognized by T cells in H-2q mice: self tolerance at the level of determinant selection

The T cell recognition of type-II collagen (CII) in H-2q mice, susceptible to CII-induced arthritis, was analyzed. With the use of T cell hybridomas derived from rat CII-immunized mice, a peptide corresponding to amino acids 245-270 on chick CII was found to harbor a T cell epitope which is present on heterologous CII (chick, rat, human, and bovine CII) but not on autologous CII. It was shown that this epitope was located within amino acids 260-270, although flanking regions in either direction were necessary for proper recognition. A peptide corresponding to human CII (256-270) was used for further studies. A single amino acid difference at position 266 between mouse CII (aspartic acid) and heterologous CII (glutamic acid) strongly influenced recognition of this peptide. No response towards the mouse peptide was seen with any of the T cell hybridomas. Inhibition studies revealed that the mouse peptide did not bind as well to major histocompatibility complex as the corresponding heterologous peptide. Both peptides gave rise to a T cell response after immunization. However, immunization with the heterologous peptide resulted in a response strictly directed to rat CII and the immunogen while immunization with the autologous peptide elicited T cells which reacted in a heteroclitic fashion, with a stronger response to the heterologous peptide than to the autologous peptide, and did respond to rat CII but not to mouse CII. We suggest that aspartic acid in position 266 results in a cryptic determinant in mouse CII which is neither recognized after CII immunization nor capable of tolerance induction. A glutamic acid at position 266, however, gives rise to an immunodominant epitope which is recognized by a large proportion of the T cells activated after immunization with heterologous CII.