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In 15 patients with multiple sclerosis (MS) and in 11 patients with other neurological diseases (OND), the phenotype of fresh unstimulated CSF and PB mononuclear cells and of "in vitro" expanded T-cells was studied by monoclonal antibody stain and cytofluorimeter analysis. A compartment-specific decrease of CD8+Leu8+ and CD8+Leu8- cells in CSF was detected; moreover, lower levels of CD8+Leu8- cells were seen in MS than in OND patients, both in CSF and in PB. Although the percentages of unstimulated CSF CD4+ cells did not differ between MS and OND, a higher proportion of "in vitro" expanded CD4+ T-cells was obtained from MS patients than from OND. Among MS patients, T-cell growth was very scarce or absent in those sampled during relapses. The results suggest alterations both within the CD4+ "helper" and the CD8+ "suppressor-cytotoxic" populations in the CSF of MS patients, and stress the relevance of functional analysis in conjunction with phenotype studies.

Autoreactive T lymphocytes were generated by culturing human peripheral blood mononuclear cells with an antigen-specific/MHC restricted autologous inducer T cell, termed RW17C and subsequently cloned in soft agar. The majority of such clones expressed the T3+T4+T8-T11+Ia+ phenotype and were directed at autologous class II MHC gene products found on B cells, macrophages and B lymphoblastoid cells as judged by their proliferative response to the latter. For this recognition, the clones employed a T3-Ti molecular complex and a T4 structure analogous to those found on allospecific T cells. Perhaps more importantly, it was observed that the same AC (autoreactive clone) induced autologous B cells to produce high levels of immunoglobulin in the absence of exogenous antigen and could synergize with the RW17C clone to effect maximal B cell Ig production. In addition, supernatant from T3-Ti triggering of AC clone induced both polyclonal proliferation and differentiation of small B lymphocytes. These results support the notion that such autoreactive cells can function in a physiologic amplifier role by facilitating induction via an internal set of signals (i.e. autologous MHC).

Recent studies using cloned antigen-specific T lymphocytes and monoclonal antibodies directed at their various surface glycoprotein components have led to the identification of the human T-cell antigen receptor as a surface complex comprised of a clonotypic 90-kD Ti heterodimer and the invariant 20- and 25-kD T3 molecules. Approximately 30,000-40,000 Ti and T3 molecules exist on the surface of human T lymphocytes. These glycoproteins are acquired and expressed during late thymic ontogeny, thus providing the structural basis for immunologic competence. The alpha and beta subunits of Ti bear no precursor-product relationship to one another and are encoded by separate genes. Moreover, the presence of unique peptides following proteolysis of different Ti molecules isolated by non-cross-reactive anticlonotypic monoclonal antibodies supports the notion that variable regions exist within both the alpha and the beta subunits. N-Terminal amino acid sequencing and molecular cloning of the Ti beta subunit further show that it bears an homology to the first V-region framework of immunoglobulin light chains and represents the product of a gene that rearranges specifically in T lymphocytes. Triggering of the T3-Ti receptor complex gives rise to specific antigen-induced proliferation through an autocrine pathway involving endogenous IL-2 production, release, and subsequent binding to IL-2 receptors. The implications of these findings for understanding human T-cell growth and its regulation in disease states are discussed.

A novel lymphokine with apparent molecular size of 10 to 12 kilodaltons is secreted from helper T cell clones within hours after cross-linking their T cell antigen-MHC (major histocompatibility complex) receptors (T3-Ti). This lymphokine, termed interleukin-4A (IL-4A), stimulates resting lymphocytes by binding to a surface component (or components) of the alternative T11 pathway and subsequently by inducing interleukin-2 (IL-2) receptors. The activation process is neither dependent on antigen specificities of the recruited population or the presence of macrophages. It appears, therefore, that IL-4A is a mediator involved in amplifying the T cell immune response.

The T lymphocyte receptor for antigen and histocompatibility molecules is a molecular complex comprised of five polypeptide chains. Both the 49KD alpha and 43KD beta chains are immunoglobulin-like and thus contain variable domains responsible for ligand binding. In contrast, the 20-25KD T3 gamma, delta and epsilon chains are monomorphic structures presumably involved in transmembrane signalling. The alpha and beta subunits are disulfide bonded to each other and held in noncovalent association with the T3 chains. T3-Ti receptor crosslinking leads to conformational modification of a second T lineage specific molecule, termed the 50KD T11 structure and in turn, protein kinase C activation, elevation in intracytoplasmic free calcium and Na+/H+ antiport stimulation.

Cerebrospinal fluid myelin basic protein and cerebrospinal fluid and peripheral blood T-cell subsets have been studied in patients with multiple sclerosis and other inflammatory and non-inflammatory nervous system diseases. These biological parameters have been correlated with clinical disease activity. No changes in peripheral blood T-cell subsets were seen in multiple sclerosis patients. Low cerebrospinal fluid T8+ cells occurred only in multiple sclerosis, while high cerebrospinal fluid T4+ cells were detected both in clinically active multiple sclerosis and in inflammatory nervous system diseases. A close relationship was found between cerebrospinal fluid T4/T8 ratio and myelin basic protein in relapsing multiple sclerosis patients.

Recent studies using cloned antigen-specific T lymphocytes and monoclonal antibodies directed at their various surface glycoprotein components have led to identification of the human T cell antigen receptor as a surface complex comprised of a clonotypic 90KD Ti heterodimer and the monomorphic 20/25KD T3 molecules. Approximately 30,000-40,000 Ti and T3 molecules exist on the surface of human T lymphocytes. These glycoproteins are acquired and fully expressed during late thymic ontogeny, thus providing the structural basis for immunologic competence. The alpha and beta subunits of Ti bear no precursor-product relationship to one another and are encoded by separate genes. The presence of unique peptides following proteolysis of different Ti molecules isolated by noncrossreactive anticlonotypic monoclonal antibodies supports the notion that variable regions exist within both the alpha and beta subunits. Moreover, N-terminal amino acid sequencing of the Ti beta subunit shows that it bears homology to the first V-region framework of immunoglobulin light chains and represents the product of a gene that rearranges specifically in T lymphocytes. Soluble or Sepharose-bound anti-Ti monoclonal antibodies, like physiologic ligand (antigen/MHC), enhanced proliferative responses to purified IL-2 by inducing a 6-fold increase in surface IL-2 receptor expression. In contrast, only Sepharose-bound anti-Ti or physiologic ligand triggered endogenous clonal IL-2 production and resulted in subsequent proliferation. The latter was blocked by antibodies directed at either the IL-2 receptor or IL-2 itself. These results suggest that induction of IL-2 receptor expression but not IL-2 release occurs in the absence of T3-Ti receptor crosslinking. Perhaps more importantly, the findings demonstrate that antigen-induced proliferation is mediated through an autocrine pathway involving endogenous IL-2 production, release, and subsequent binding to IL-2 receptors.

The cellular origin of B cell growth factors (BCGF) and differentiation factors (BCDF) was investigated in the present study. For this purpose, T4+ and T8+ T cell clones were obtained from human peripheral blood, activated via stimulation of either the antigen/MHC receptor (T3-Ti molecular complex) or the antigen-independent alternative pathway (T11 molecule), and subsequently examined for their capacity to induce B cell proliferation and immunoglobulin production. The results showed that 1) BCGF is produced by both T4+ and T8+ T cells at the population level as well as at the clonal level; 2) BCDF activity, in contrast, is largely but not exclusively restricted to the T4+ subset; and 3) both the T3-Ti and T11 pathways activate individual clonal T cell populations to promote B cell growth and differentiation.

Considerable evidence now exists to support the notion that the 50-kDa sheep erythrocyte-binding protein, T11, represents an essential cell surface component of a human T-cell lineage activation pathway. Furthermore, it is known that the human T3-Ti T-cell antigen/major histocompatibility complex receptor complex is capable of regulating cell growth mediated by the T11 structure. Here we show that, within the T3+ thymocyte compartment, T3-Ti crosslinking rapidly inhibits T11-initiated interleukin 2 (IL-2) gene transcription and translation. This inhibition is restricted to the IL-2 gene (IL2) as transcription of both the IL-2-receptor gene (IL2R) and the Ti beta-chain gene (TCRB) are not affected (human gene designations are in parentheses). Perhaps more importantly, T3-Ti-mediated IL-2 inhibition of this type is not operational in peripheral T lymphocytes. The results imply that the majority of T3+ thymocytes are functionally distinct from peripheral T lymphocytes despite their T3+ phenotype and must possess a unique endogenous regulatory component for suppressing IL-2 gene activity. Moreover, since IL-2 is likely rate-limiting for growth within the thymus, the findings provide one plausible mechanism for thymic selection--namely, T3-Ti crosslinking of thymocytes upon interaction with self-major histocompatibility complex inhibits clonal expansion of high-affinity autoreactive cells.