Interleukin-2 signals during priming are required for secondary expansion of CD8+ memory T cells

Although interleukin-2 (IL-2) was initially characterized as the primary T-cell growth factor following in vitro activation, less is known about its role in shaping T-cell responses to acute infections in vivo. The use of IL-2- or IL-2-receptor-deficient mice is problematic owing to their early development of autoimmunity, attributable to the central role of IL-2 in the generation, maintenance and function of CD4+CD25+ regulatory T cells. To bypass these inherent difficulties, we have studied the effect of IL-2 on T-cell responses to acute infections by adopting a mixed chimaera strategy in which T cells lacking the high-affinity IL-2 receptor could be studied in an otherwise healthy mouse containing a full complement of regulatory T cells. Here we show that although IL-2 signalling to pathogen-specific CD8+ T cells affects the number of developing effector and memory cells very little, it is required for the generation of robust secondary responses. This is not due to an altered T-cell-receptor repertoire development or selection, and does not reflect an acute requirement for IL-2 during secondary activation and expansion. Rather, we demonstrate a previously unappreciated role for IL-2 during primary infection in programming the development of CD8+ memory T cells capable of full secondary expansion. These results have important implications for the development of vaccination or immunotherapeutic strategies aimed at boosting memory T-cell function.     

Epstein-Barr virus genome-positive T lymphocytes in a boy with chronic active EBV infection associated with Kawasaki-like disease

Epstein-Barr virus (EBV), a ubiquitous human herpesvirus and an aetiological agent of infectious mononucleosis, has a unique tropism for B lymphocytes. Clinical and laboratory features of chronic active EBV infections are chronic or persistent infectious mononucleosis-like symptoms and high antibody titre against early antigens (EA). Kawasaki disease (KD), aetiology unknown, is thought to be self-limited immunologically mediated vasculitis. Clinical features of KD are fever, rash, mucositis, lymphadenopathy and coronary artery damage. We report here a child with chronic active EBV infection accompanied by dilatation of coronary arteries. All the EBV-determined nuclear antigen (EBNA)-positive lymphocytes had exclusively CD4 antigen, as revealed by dual staining immunofluorescence analysis. Southern blot hybridization showed that the purified CD4+ cells harboured EBV genome.     

Lymphocytes bearing antigen-specific gamma delta T-cell receptors accumulate in human infectious disease lesions

The majority of T cells bear the T-cell receptor (TCR) alpha beta complex which recognizes foreign antigen peptides only in the context of self major histocompatibility complex (MHC) molecules. Such T cells function in a variety of effector roles and secrete cytokines that mediate the activation and differentiation of other cells in the immune system. Recently, a small subpopulation T cells was found to bear a distinct TCR composed of gamma and delta subunits. In man, TCR gamma delta+ cells are distributed as approximately 5 per cent of the CD3+ cells in all organized lymphoid organs as well as in the skin- and gut-associated lymphoid tissues. Although a limited number of germ-line genes encode the TCR gamma and delta subunits, extensive junctional variation particularly in the delta gene, results in unprecedented diversity for this receptor. The nature of the specificity and immunological functions of these T cells remains enigmatic. We report here that in contrast to the normal low frequency of gamma delta-bearing cells in lymphoid tissues, peripheral blood, or normal skin, the frequency is increased five to eightfold in particular granulomatous reactions of leprosy. TCR gamma delta+ lymphocyte lines from these leprosy skin lesions proliferate in vitro specifically to mycobacterial antigens. This reactivity to foreign antigens appears to require presentation in the context of self-molecules. Moreover, culture supernatants from activated gamma delta T lymphocytes induce adhesion and aggregation of bone-marrow monocytes in the presence of granulocyte monocyte-colony stimulating factor (CSF), suggesting that products of gamma delta-bearing T cells may play a role in the immune response, possibly by stimulating granuloma formation.     

Accessory cell-dependent selection of specific T-cell functions

Activation of many T-cell functions depends on their interaction with antigen-presenting accessory cells which express I region associated (Ia) products. Cells expressing accessory cell function include those of the monocyte/macrophage lineage and dendritic cells. More recently, B cells and a number of tumour cell lines of macrophage or B-cell origin were shown to act as accessory cells in certain assays. We showed previously that normal peritoneal exudate macrophages (PEC) induced both T-cell proliferation as well as T-cell help, whereas various Ia+ tumour lines of macrophage or B-cell origin, although stimulating antigen-specific T-cell proliferation, did not significantly activate T-cell help. We report here that during the initial T-cell activation in vitro accessory cells (PEC or Ia+ tumour cells) select particular T cells to express previously determined functions. Moreover, some tumour cell lines induce suppressor T cells which inhibit helper activity.     

Alternative pathway activation of T cells by binding of CD2 to its cell-surface ligand

Activation of resting T lymphocytes is initiated by the interaction of cell-surface receptors with their corresponding ligands. In addition to activation through the CD3 (T3)-Ti antigen-receptor complex, recent experiments have demonstrated induction of T-cell proliferation through the CD2 (T11) molecule, traditionally known as the erythrocyte(E)-receptor, through which T cells can bind red blood cells (RBC). This 'alternative pathway' of T-cell activation was observed in vitro in response to combinations of anti-CD2 monoclonal antibodies (mAbs) that bind to distinct epitopes of CD2, such as mAbs against T11(2) plus T11(3). The physiological importance of this activation pathway can be assessed only by studying the effects of a naturally occurring ligand of CD2 on T-cell activation. We have recently described such a ligand, a glycoprotein of apparent relative molecular mass 42,000 (Mr 42K) that is expressed on all blood cells and some other tissues. Here we demonstrate that binding of this cell surface molecule, termed T11 target structure or T11TS, to CD2 (T11) induces reactivity in resting T cells to a mitogenic stimulus given by a mAb to the T11(3) determinant or by submitogenic concentrations of anti-T11(2+3) mAbs. Thus, one of the signals required for T-cell activation through the alternative pathway is provided by the interaction of CD2 with a naturally occurring complementary cell-surface molecule.     

Stimulation of oligodendroglial proliferation and maturation by interleukin-2

There exists considerable evidence that the growth of glial cells can be influenced by T-cell-derived lymphokines and monokines. Astrocytes proliferate in the presence of mitogen- or antigen-stimulated T-cell supernatants, supernatants from human T-lymphotropic virus (HTLV)-transformed T cells, and purified human interleukin-1 (IL-1; ref. 4). Oligodendrocytes proliferate and differentiate when incubated with supernatants from mitogen-activated or HTLV-transformed T cells. In addition, we have recently purified a T-cell-derived lymphokine of relative molecular mass 30,000, termed glial growth promoting factor (GGPF), which specifically stimulates the proliferation of oligodendrocytes. The traditional role of interleukins 1 and 2 is in the initiation, propagation and regulation of the immune response. IL-1, released by a variety of cells including monocytes, stimulates T cells to produce IL-2; IL-2 in turn induces the expansion of T cells that is critical for immune responsiveness. Recently, IL-2 has been shown to induce B-cell proliferation and immunoglobulin secretion, indicating that its action is not restricted to T cells. We now report that recombinant human IL-2 influences the growth of glial cells--specifically, the proliferation and differentiation of oligodendrocytes. IL-2 may have a role in the inflammatory neural lesions of multiple sclerosis patients and in the growth of brain glia during injury or disease.     

No T-cell tyrosine protein kinase signalling or calcium mobilization after CD4 association with HIV-1 or HIV-1 gp120.

The T lymphocyte surface protein CD4 is an integral membrane glycoprotein noncovalently associated with the tyrosine protein kinase p56lck. In normal T cells, surface association of CD4 molecules with other CD4 molecules or other T-cell surface proteins, such as the T-cell antigen receptor, stimulates the activity of the p56lck tyrosine kinase, resulting in the phosphorylation of various cellular proteins at tyrosine residues. Thus, the signal transduction in T cells generated through the surface engagement of CD4 is similar to that observed for the class of growth factor receptors possessing endogenous tyrosine kinase activity. As CD4 is also the cellular receptor for the human immunodeficiency virus (HIV), binding of the virus or gp120 (the virus surface protein responsible for specific CD4+ T-cell association) could mimic the types of immunological interactions that have previously been found to stimulate p56lck and trigger T-cell activation pathways. We have evaluated this possibility and report here that binding of HIV-1 or the virus glycoprotein gp120 to CD4+ human T cells fails to elicit detectable p56lck-dependent tyrosine kinase activation and signalling, alterations in the composition of cellular phosphotyrosine-containing proteins, or changes in intracellular Ca2+ concentration.     

A suppressor T-lymphocyte cell line for autoimmune encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is a model for the in vitro and in vivo study of T-cell activation. It is an autoimmune disease mediated by T lymphocytes of the helper T-cell (Th) subset. After sensitization to guinea-pig myelin basic protein in complete Freund's adjuvant, Lewis rats develop an autoimmune response to central nervous system (CNS) myelin basic protein, manifested clinically as paralysis and histologically by a perivascular mononuclear cell infiltrate of the CNS parenchyma. Suppressor cell regulation of EAE has long been suspected because Lewis rats, which spontaneously recover from active disease, are resistant to reinduction of active EAE, even though effector T-cell lines can be rescued from these recovered rats. Using cyclosporin A, an immunosuppressive agent believed to inhibit Th cell function, suppressor T-cell (Ts) lines have now been generated from recovered Lewis rats. These Ts cells, when admixed with guinea pig myelin basic protein-specific Th cells, will prevent the adoptive transfer of EAE. The Ts cells appear to be CD4+, which explains previous observations that CD8+ lymphocytes are not important in the recovery of EAE in the rat. This is the first direct demonstration of Ts-cell regulation of EAE.     

Activation of cytolytic T lymphocyte and natural killer cell function through the T11 sheep erythrocyte binding protein

The T11 sheep erythrocyte binding glycoprotein [relative molecular mass (Mr)50,000(50K)] is expressed throughout human T-lymphocyte ontogeny and appears to play an important physiological role in T-cell activation. Thus, the treatment of T cells with certain monoclonal anti-T11 antibodies results in antigen-independent polyclonal T-cell activation as assessed by proliferation and lymphokine secretion. In addition, the majority of thymocytes that have not yet acquired the T3-Ti antigen/major histocompatibility complex (MHC) receptor can be activated to express interleukin-2 (IL-2) receptors through this T11 structure. We show here that the triggering of cytolytic T (Tc) cells via T11 causes an antigen-independent activation of the cytolytic mechanism as evidenced by the induction of nonspecific cytolytic activity. Furthermore, T11+T3-Ti- natural killer (NK) cell clones can also be induced to lyse NK-cell-resistant targets by treatment with anti-T11 monoclonal antibodies directed at defined T11 epitopes. These results indicate that T11 triggering can activate cytotoxic lymphocytes to express their functional programmes in the absence of specific antigen recognition via the T3-Ti complex and provide further evidence for the notion that certain NK cells and T lymphocytes are related.     

Positive and negative selection of an antigen receptor on T cells in transgenic mice

The T-cell repertoire found in the periphery is thought to be shaped by two developmental events in the thymus that involve the antigen receptors of T lymphocytes. First, interactions between T cells and major histocompatibility complex (MHC) molecules select a T-cell repertoire skewed towards recognition of antigens in the context of self-MHC molecules. In addition, T cells that react strongly to self-MHC molecules are eliminated by a process called self-tolerance. We have recently described transgenic mice expressing the alpha beta T-cell receptor from the cytotoxic T lymphocyte 2C (ref. 11). The clone 2C was derived from a BALB.B (H-2b) anti-BALB/c (H-2d) mixed lymphocyte culture and is specific for the Ld class I MHC antigen. In transgenic H-2b mice, a large fraction of T cells in the periphery expressed the 2C T-cell receptor. These T cells were predominantly CD4-CD8+ and were able to specifically lyse target cells bearing Ld. We now report that in the periphery of transgenic mice expressing Ld, functional T cells bearing the 2C T-cell receptor were deleted. This elimination of autoreactive T cells appears to take place at or before the CD4+CD8+ stage in thymocyte development. In addition, we report that in H-2s mice, a non-autoreactive target haplotype, large numbers of CD8+ T cells bearing the 2C T-cell receptor were not found, providing strong evidence for the positive selection of the 2C T-cell receptor specificity by H-2b molecules.     

A molecular clone of HTLV-III with biological activity

Acquired immune deficiency syndrome (AIDS) is an epidemic immunosuppressive disease characteristically associated with a depletion of T lymphocytes of the helper/inducer phenotype. Numerous converging lines of research have implicated a human T-cell lymphotropic retrovirus, HTLV-III, in the pathogenesis of AIDS. Recently, several distinct forms of the HTLV-III genome were molecularly cloned in phage and extensively characterized. In the present study, a clone containing full-length HTLV-III proviral DNA was inserted into a plasmid and used to transfect cord blood T cells from normal newborn humans. We demonstrate that this molecular clone is infectious in vitro and causes marked cytopathic effects on T-cell cultures. This is the first direct evidence that the HTLV-III genome, rather than a minor component of the virus complex, is cytopathic for T cells. Using this biologically competent clone and mutants derived from it, it should now be possible to localize the subgenomic regions that contribute to the biological effects of HTLV-III.     

Activation-independent binding of human memory T cells to adhesion molecule ELAM-1.

The induction of an ensemble of adhesion molecules on endothelial cells by inflammatory cytokines is likely to be crucial to the differential migration of T-lymphocyte subsets into inflammatory sites. Two molecular pathways involving the VLA-4 and LFA-1 integrins are known to mediate T-cell adhesion to activated endothelium. Here we show that a third pathway involving the rapidly inducible endothelial cell-surface adhesion molecule ELAM-1 contributes to the binding of resting CD4+ T cells to IL-1-induced human endothelial cells. All three pathways contribute to the greater adhesion to endothelium of memory T cells than naive T cells. There are two unique features of T-cell adhesion to purified ELAM-1: first, ELAM-1 exclusively mediates adhesion of memory T cells; second, memory T-cell binding to ELAM-1 is independent of acute activation events that regulate integrin-mediated adhesion. Thus, ELAM-1 may be of primary importance in the initial attachment of memory T cells to inflamed endothelium in vivo and to the preferential migration of memory T cells into tissue and inflammatory sites.     

Recovery from autoimmunity of MRL/lpr mice after infection with an interleukin-2/vaccinia recombinant virus

Interleukin-2 (IL-2) is a T-cell derived molecule implicated in the clonal expansion of antigen-activated T cells and in T-cell development. IL-2 is also implicated in autoimmune disease, although its role is still controversial. Murine systemic lupus erythematosus (SLE) is a good model for human SLE as most of the immunological abnormalities in the human disease also seem to be operative in the mouse. Among SLE mice, the MRL/lpr strain develops early in life autoimmune diseases such as immune complex-mediated glomerulonephritis, arthritis and arteritis. Lymphoid abnormalities associated with those diseases in this strain are thymic atrophy and abnormal proliferation of CD3+ CD4- CD8- 'double-negative' T cells, resulting in massive generalized lymph node enlargement. We have therefore now examined the effects of IL-2 on the disease progression in MRL/lpr mice using live vaccinia recombinant viruses expressing the human IL-2 gene. Vaccinated mice showed prolonged survival, decreased autoantibody and rheumatoid factor titres, marked attenuation of kidney interstitial infiltration and intraglomerular proliferation, as well as clearance of synovial mononuclear infiltrates. Inoculation with the IL-2/vaccinia recombinant virus led, in addition, to drastic reduction of the double-negative T-cell population, improved thymic differentiation and restoration of normal values of mature cells in peripheral lymphoid organs.     

Control of B-cell responses by Toll-like receptors

Toll-like receptors (TLRs) detect microbial infection and have an essential role in the induction of immune responses. TLRs can directly induce innate host defence responses, but the mechanisms of TLR-mediated control of adaptive immunity are not fully understood. Although TLR-induced dendritic cell maturation is required for activation of T-helper (T(H)) cells, the role of TLRs in B-cell activation and antibody production in vivo is not yet known. Here we show that activation and differentiation of T(H) cells is not sufficient for the induction of T-dependent B-cell responses. We find that, in addition to CD4+ T-cell help, generation of T-dependent antigen-specific antibody responses requires activation of TLRs in B cells.     

Immunization with a synthetic T-cell receptor V-region peptide protects against experimental autoimmune encephalomyelitis

T cells expressing the alpha beta T-cell receptor (TCR) for antigen can elicit anti-idiotypic antibodies specific for the TCR that regulate T-cell function. Defined sequences of the TCR, however, have not been used to elicit specific antibodies and the role of cellular immunity directed against TCR determinants has not been studied. We immunized Lewis rats with a synthetic peptide representing a hypervariable region of the TCR V beta 8 molecule. Subsequent induction of experimental autoimmune encephalomyelitis, a paralytic disease of the central nervous system mediated primarily by V beta 8+ T cells specific for myelin basic protein was prevented. T cells specific for the TCR V beta 8 peptide conferred passive protection against the disease to naive rats, apparently by shifting the predominant T-cell response away from the major encephalitogenic epitope of basic protein. This is the first report demonstrating the use of a synthetic TCR V-region peptide to induce specific regulatory immunity and has important implications for the regulation of human disease characterized by common TCR V-gene usage.     

Abnormal differentiation of thymocytes in mice treated with cyclosporin A

Cyclosporin A (CsA) acts as a powerful immunosuppressive agent, and also, when given in repeated doses, can cause T-cell-dependent graft-versus-host disease and organ-specific autoimmune disease in rodents. This suggests that CsA interferes with the processes governing self-tolerance, either by nullifying the activity of T suppressor cells or by preventing the deletion of autoreactive T cells during ontogeny in the thymus. We report here that irradiated mice given repeated injections of CsA show striking dysfunction of the thymus. There are two different effects, the first of which is that CsA seems to block the differentiation of immature CD4+CD8+ thymocytes into mature CD4+CD8- and CD4-CD8+ cells expressing a high density of T-cell receptors and CD3 molecules. Second, CsA-treated mice show incomplete deletion of T cells expressing T-cell receptor molecules reactive to self H-2 I-E molecules.     

An AIDS-related cytotoxic autoantibody reacts with a specific antigen on stimulated CD4+ T cells

Patients with the acquired immune deficiency syndrome (AIDS) and AIDS-related conditions are known to have abnormalities of T cell subpopulations, including a decreased helper/inducer (bearing the CD4 antigen) to suppressor/cytotoxic (bearing the CD8 antigen) T cell ratio and decreased absolute numbers of T cells with the CD4+ phenotype. Infection of T cells with a retrovirus, termed human immunodeficiency virus (HIV), is thought to be important in these abnormalities. HIV infection alone does not adequately explain the CD4+ T-cell abnormalities seen in AIDS, however, and the nature of T-cell destruction in this disease remains poorly characterized. Here we describe an AIDS-related serum autoantibody that reacts with an antigen of relative molecular mass 18,000 (Mr 18K) restricted to lectin-stimulated or HIV-infected CD4+ T cells. The antibody also suppresses proliferation of CD4+ T cells in vitro and induces cytotoxicity of these cells in the presence of complement. Its role in the development of AIDS merits attention.     

Dominant influence of HLA-B in mediating the potential co-evolution of HIV and HLA

The extreme polymorphism in the human leukocyte antigen (HLA) class I region of the human genome is suggested to provide an advantage in pathogen defence mediated by CD8+ T cells. HLA class I molecules present pathogen-derived peptides on the surface of infected cells for recognition by CD8+ T cells. However, the relative contributions of HLA-A and -B alleles have not been evaluated. We performed a comprehensive analysis of the class I restricted CD8+ T-cell responses against human immunodeficiency virus (HIV-1), immune control of which is dependent upon virus-specific CD8+ T-cell activity. In 375 HIV-1-infected study subjects from southern Africa, a significantly greater number of CD8+ T-cell responses are HLA-B-restricted, compared to HLA-A (2.5-fold; P = 0.0033). Here we show that variation in viral set-point, in absolute CD4 count and, by inference, in rate of disease progression in the cohort, is strongly associated with particular HLA-B but not HLA-A allele expression (P < 0.0001 and P = 0.91, respectively). Moreover, substantially greater selection pressure is imposed on HIV-1 by HLA-B alleles than by HLA-A (4.4-fold, P = 0.0003). These data indicate that the principal focus of HIV-specific activity is at the HLA-B locus. Furthermore, HLA-B gene frequencies in the population are those likely to be most influenced by HIV disease, consistent with the observation that B alleles evolve more rapidly than A alleles. The dominant involvement of HLA-B in influencing HIV disease outcome is of specific relevance to the direction of HIV research and to vaccine design.