T cell- and B cell-independent adaptive immunity mediated by natural killer cells

It is commonly believed that only T lymphocytes and B lymphocytes expressing recombination-dependent antigen-specific receptors mediate contact hypersensitivity responses to haptens. Here we found that mice devoid of T cells and B cells demonstrated substantial contact hypersensitivity responses to 2,4-dinitrofluorobenzene and oxazolone. Those responses were adaptive in nature, as they persisted for at least 4 weeks and were elicited only by haptens to which mice were previously sensitized. No contact hypersensitivity was induced in mice lacking all lymphocytes, including natural killer cells. Contact hypersensitivity responses were acquired by such mice after adoptive transfer of natural killer cells from sensitized donors. Transferable hapten-specific memory resided in a Ly49C-I(+) natural killer subpopulation localized specifically in donor livers. These observations indicate that natural killer cells can mediate long-lived, antigen-specific adaptive recall responses independent of B cells and T cells.     

T cell-independent B cell memory

Despite being unable to mount a bona fide recall antibody (Ab) response to secondary immunization, T cell-independent antigens (TI Ag) such as pneumococcal capsular polysaccharides (PS) can generate protective humoral immunity in adults. The concept of TI B cell memory after being iconoclastic for decades has now received experimental support from several laboratories. TI B cell memory comprises two components: i) memory B lymphocytes that differ phenotypically and functionally from their T cell-dependent counterparts, ii) memory bone marrow plasma cells that play a crucial role in the immune protection conferred by TI polysaccharidic vaccines. B-1b cells constitute the major source of both TI memory lymphocytes and plasma cells. This conceptual shift should lead to rehabilitate the TI arm of the immune system for vaccination purposes.     

T cell-independent development of B memory cells

Speen cells derived from sheep red blood cell (SRBC)-primed nude mice gave a typical secondary response when challenged in vitro with SRBC in the presence of SRBC-primed T cells. The results demonstrate that B memory cells of both IgM and IgG type develop in the absence of functioning T cells. Moreover, these results indicate that Θ-antigen-bearing cells, reactive to phytohemagglutinin (PHA) or concanavalin A (Con A), are not involved in the initiation of B cell triggering, but rather in the differentiation step leading to antibody-forming cells.     

Properties of lymphocytes which confer adoptive immunity to tuberculosis in rats

Following immunization of rats with BCG there was added to thoracic duct lymph a population of sensitized lymphocytes which conferred adoptive immunity to tuberculosis upon syngeneic recipients. At an early stage of immunization, 5 days after BCG inoculation, the sensitized cells were large and medium lymphocytes as evidenced by their sensitivity to vinblastine. On day 8, the sensitized cell population was partially resistant to vinblastine and by day 28 it was totally resistant. The vinblastine resistant cells have the functional properties of small lymphocytes, since they recirculate freely from the blood to lymph, and can confer long lasting immunity upon recipient rats.

The data imply that protective immunity against the tubercle bacillus is transferred by a family of newly-formed lymphocytes, the most immature of which are immunoblasts or large lymphocytes. As the response matures, sensitized small lymphocytes are delivered to the circulation and comprise an increasing proportion of the protective cell population.

     

T cell receptor-dependent activation of human lymphocytes through cell surface ganglioside GT1b: implications for innate immunity

Gangliosides form a component of the glycosphingolipid-rich membrane microdomains recently shown to play an important role in receptor signal transduction. Specific gangliosides also serve as receptors for binding and internalization of bacterial toxins. In the course of characterizing the basis of the native tetanus toxin (TTx) reactivity of a human gamma delta T cell clone, we observed that transfer of the TCR was required to impart TTx reactivity on a TCR-negative recipient T cell. However, the reconstitution of toxin reactivity could be achieved regardless of the antigen specificity of the TCR chains. Further analysis showed that the T cell recognition of native TTx was dependent on the presence of its ganglioside receptor, GT1b, on the T cell surface. Incorporation of exogenous GT1b into plasma membrane conferred TTx reactivity on otherwise non-reactive T cells provided these cells expressed the TCR. Finally, reconstitution of TCR-negative Jurkat T cells with a CD8-CD3zeta chain chimera demonstrated that the cytoplasmic region of the CD3zeta chain was sufficient to couple ganglioside-mediated TTx binding to T cell activation. These data reveal a novel mode of TCR-dependent reactivity to a bacterial toxin that could mobilize a large subset of T cells, thus representing a form of innate immunity. Given the possibility that endogenous ligands may bind to cell surface gangliosides, regulation of their levels and topology on the cell surface may constitute an immunoregulatory mechanism.     

T cell-independent and toll-like receptor-dependent antigen-driven activation of autoreactive B cells

On the lupus-prone MRL-lpr/lpr (MRL-lpr) background, AM14 rheumatoid factor (RF) B cells are activated, differentiate into plasmablasts, and undergo somatic hypermutation outside of follicles. Using multiple strategies to impair T cells, we found that such AM14 B cell activation did not require T cells but could be modulated by them. In vitro, the signaling adaptor MyD88 is required for IgG anti-chromatin to stimulate AM14 B cell proliferation when T cells are absent. However, the roles of Toll-like receptors (TLRs) in AM14 B cell activation in vivo have not been investigated. We found that activation, expansion, and differentiation of AM14 B cells depended on MyD88; however, mice lacking either TLR7 or TLR9 displayed partial defects, indicating complex roles for these receptors. T cell-independent activation of certain autoreactive B cells, which gain stimuli via endogenous TLR ligands instead of T cells, may be the initial step in the generation of canonical autoantibodies.     

Adoptive transfer of immunity to Plasmodium berghei with immune T and B lymphocytes.

Immunity to malarial infection may be transferred with immune lymphocytes. This study was designed to determine which lymphocyte type is responsible for the adoptive transfer of immunity to malarial infection. In one set of experiments, the ability of immune T and B lymphocytes, separated by passage through nylon-wool columns, to transfer immunity to infection was determined. In another experiment, the effect of killing T lymphocytes with anti-theta serum on the transfer of immunity was determined. The effect on the ability of immune lymphocyte suspensions to transfer immunity after B lymphocytes were removed from such suspensions by centrifugation on Ficoll-Hypaque gradients, after they had formed rosettes with sensitized, complement-coated sheep erythrocytes, was also determined. The ability of lymphocyte suspensions to adoptively transfer resistance to malarial infection was greatly impaired by the removal from the suspensions of differentiated B-type lymphocytes. Our results indicate that it is the differentiated B cell, most probably an antibody-producing cell, which lacks both theta antigen and the complement receptor that is responsible for conferring immunity to malaria.     

T cell-independent somatic hypermutation in murine B cells with an immature phenotype

Somatic hypermutation contributes to the generation of antibody diversity and is strongly associated with the maturation of antigen-specific immune responses. We asked whether somatic hypermutation also plays a role in the generation of the murine immunoglobulin repertoire during B cell development. To facilitate identification of somatic mutations, we examined mouse systems in which only antibodies expressing lambda1, lambda2, and lambdax light chains can be generated. Somatic mutations were found in cells, which, by surface markers, RAG expression, and rapid turnover, had the phenotype of immature B cells. In addition, expression of AID was detected in these cells. The mutations were limited to V regions and were localized in known hotspots. Mutation frequency was not diminished in the absence of T cells. Our results support the idea that somatic hypermutation can occur in murine immature B cells and may represent a mechanism for enlarging the V gene repertoire.     

Abnormal B cell response to T cell-independent polyclonal B cell activators in haemophilia A.

In addition to T cell abnormalities, patients with haemophilia A show a separate B cell dysfunction. Characteristic are elevated spontaneous IgG (not IgM) levels in the patient's sera and in the culture supernatants of peripheral blood mononuclear cells. It is also observed that these cells fail to show a differentiation response to T cell-independent B cell activators. The B cell dysfunction correlates with the amount of factor VIII concentrates given prophylactically to patients with severe haemophilia. In contrast to the acquired immune deficiency syndrome (AIDS), the proliferation response to B cell mitogens is not affected.     

Cell-mediated immunity against epstein-barr virus infected B lymphocytes

Conclusions Studies on cell-mediated immunity against EB virus and EBV transformed B cells provide one of the most interesting and accessible systems for analyzing the host response against a transforming virus, and against its premalignant and malignant cellular products. The survival of the present EBV strain in the human species is probably a consequence of its restricted infectivity for B cells. Due to this a control mechanism against the proliferation of the infected cells is a functional component of the immune system and is available before antigen-specific immunity can develop.     

Cytotoxic T lymphocytes, chemokines and antiviral immunity.

Evidence that CD8+ CTLs produce chemokines following engagement of viral antigens, and that MIP-1alpha is required for an inflammatory response to virus challenge, suggests that these molecules are key elements in the generation of effective antiviral immunity. Here, David Price and colleagues argue that the antigen-dependent release of chemokines by CTLs provides an elegant mechanism linking localization, amplification and coordination of the antiviral immune response to specific recognition of infected host cells beyond the confines of the lymphoid system.     

T and B lymphocytes in pregnancy

Summary The proportion of human peripheral B- and T-lymphocytes of pregnant women was studied by immunofluorescence and rosette tests. No significant difference between pregnant women and controls was found in the absolute number of circulating T-cells. A slight increase in the absolute number of B-cells was observed in pregnancy. The percentage of total RFC was the same in pregnant women and in controls whereas the percentage of stable RFC and PHA induced RFC decreased in pregnancy. The conclusion of the results was drawn that the depression of maternal immunity may depend on other factors than the decreased proliferation of T-cells.     

Stress proteins and immunity mediated by cytotoxic T lymphocytes

Chaperone molecules, including members of the heat shock protein family, are able to stimulate alphabeta and gammadelta T cells as well as natural killer cells. For alphabeta T cells, specificity is induced by chaperone-assisted peptides; this has lead to detailed investigations of peptides that bind to these chaperones and their possible role in antigen presentation.     

Parameters governing exhaustion of rare T cell-independent neutralizing IgM-producing B cells after LCMV infection

The late appearance of neutralizing antibodies (nAb) against lymphocytic choriomeningitis virus (LCMV) has been attributed to various factors including immunopathology, low frequency of high-affinity specific B cells and competition by nonspecific polyclonal B cell activation. To investigate the activation of LCMV-nAb-producing B cells early following infection, we performed adoptive transfers of LCMV-specific B cells into WT recipients. By modulating parameters such as viral load, number of specific B cells and presence of T cell help, we found that a high antigen-to-B cell ratio led to normal IgM responses. IgG and memory response however, were impaired as most nAb-producing B cells rapidly terminally differentiated into short-lived IgM plasma cells. Lowering the antigen-to-B cell ratio, or increasing the level of T cell help, could rescue the class-switched antibody response. Upon infection, a low frequency of LCMV-nAb-producing B cells, as observed in WT mice, results in a high antigen-to-B cell ratio and is likely to lead to terminal differentiation - and elimination - of these rare B cells.     

Tyrosine phosphorylation of α tubulin in human T lymphocytes

N-terminal sequencing of the 55- and 50-kDa polypeptides affinity purified on a phosphotyrosine monoclonal antibody column from activated Jurkat T cells identified α and β tubulin. Two-dimensional gel analysis indicated that α tubulin was directly phosphorylated on tyrosine. β Tubulin was not detectably tyrosine phosphorylated but was precipitated by anti-phosphotyrosine (PTyr) antibody by virtue of its association with the α subunit as a heterodimer. Phosphotyrosyl α tubulin was not incorporated into intact microtubules and was all in the unpolymerized soluble fraction. These results suggest that tyrosine phosphorylation of α tubulin may inhibit the ability of this subunit to polymerize into microtubules. Stimulation of Jurkat T cells via T cell receptor increased the amount of tubulin precipitated by the anti-PTyr antibody. These data raise the possibility that the polymerization of tubulin heterodimers may be regulated by phosphorylation on tyrosine during T cell activation.     

Particle-mediated DNA immunization of cattle confers long-lasting immunity against bovine herpesvirus-1

Particle-mediated delivery was used as a method to vaccinate ruminants with a DNA vaccine. The optimal conditions for gene gun-based delivery of gold particles into the epidermal layer of the skin were determined. After delivery of the gold particles, an inflammatory response was observed. This response occurred regardless of the presence of plasmid and therefore was a result of the physical disturbance of the skin by the gold particles. To identify transfected cells, a plasmid expressing a green fluorescent protein was delivered into the skin. Fluorescent cells were located primarily in the outermost layers of the epidermis and outside the core of gold particles deposited by the gene gun. Cattle were immunized by gene gun with a plasmid expressing a truncated, secreted form of bovine herpesvirus-1 glycoprotein D. Serum antibody responses, antigen-specific proliferation, and interferon-gamma secretion by peripheral blood lymphocytes were demonstrated. These immune responses were found to be of long duration and sufficient magnitude to protect cattle against challenge with bovine herpesvirus-1, which demonstrates the efficacy of gene gun-based delivery of DNA vaccines to target species.     

Haptenated streptococcal antigens elicit either T cell-dependent type 1 or T cell-independent type 2 immune responses

Antigens of Streptococcus mutans 6715 (alternatively designated serotype g Streptococcus sobrinus), including whole cells (WC g), cell walls (CW g), peptidoglycan (PG g) and serotype carbohydrate (Ml g) were coupled with trinitrophenyl (TNP), and the nature of the immune response to each immunogen was determined in normal and X-linked immunodeficient (xid) murine spleen cell cultures. Responses to TNP-WC g, -CW g and -PG g and to the classical type 1 antigen TNP-Brucella abortus occurred in both xid and normal splenic cultures, while TNP-Ml g only triggered immune responses in normal spleen cell cultures, suggesting that the former three antigens are type 1 and the latter type 2. Further support for the type 2 nature of TNP-Ml g was the finding that Peyer's patch cell cultures from both xid (which contain mature B cells) and normal mice supported responses to TNP-Ml g and TNP-Ficoll, while xid splenic cultures failed to support responses to either type 2 antigen. The three type 1 TNP-S. mutans antigens induced responses in nude spleen cell and in purified splenic B cell cultures, but required T cells for in vitro responses to lower doses of immunogen. On the other hand, TNP-Ml g induced anti-TNP PFC responses at several antigen concentrations in purified B cell cultures, without requirement for added T cells. These studies show that the intact S. mutans cell, as well as CW g and PG g, acts as a T cell-dependent (TD) type 1 antigen, while the serotype carbohydrate (Ml g) induces a T cell-independent (TI) type 2 response. Thus, the intact bacterium is a TD type 1 antigen, whereas its purified components are either type 1 or type 2 antigens and differ significantly in terms of their T cell dependence.