T cell response to staphylococcal superantigens by asymptomatic HIV-infected individuals exhibits selective changes in T cell receptor V beta-chain usage

B cell-mediated infection of stimulated and unstimulated autologous T lymphocytes with HIV-1: role of complement

In vivo, human immunodeficiency virus type 1 (HIV-1) is opsonized with complement fragments and virus-specific antibodies (Ab). Thus, HIV is able to interact with complement receptor (CR) - and Fc receptor (FcR) - positive cells such as B cells, follicular dendritic cells or macrophages. In this study we demonstrate that the interaction between B cells and HIV has an impact on autologous primary T cell infection in vitro. We confirmed the presence of complement-fragments and virus-specific Ab on serum-treated HIV using a virus-capture assay. In experiments with CR2-specific Ab we showed that the virus/B cell interaction was mainly dependent on CR2. In infection experiments immobilisation of HIV on stimulated tonsil B cells greatly enhanced the infection of interleukin (IL)-2-activated autologous tonsil T cells. Surprisingly, enhancement of T cell infection by B cell-HIV complexes was observed even in the absence of mitogenic stimuli such as PMA and was independent of the addition of exogenous IL-2. Taken together, these results indicate that primary B cells are able to efficiently transmit opsonised HIV to autologous primary T cells and induce a massive enhancement of infection. These in vitro experiments mimic the in vivo situation in the lymphoid tissue and suggest an alternative mechanism for the infection of primary T cells.

Superantigens as virulence factors in autoimmunity and immunodeficiency diseases

Virulence factors are microbial products that are known to be harmful to the host and may assist in the pathogenesis of the micro-organism. Superantigens, including those produced by bacteria and viruses, clearly act as virulence factors. The clinical effects of superantigens can be not only acute but also chronic and complex. Recent evidence suggests that superantigens may play a central role in the pathogenesis of autoimmune and immunodeficiency disorders. It is our contention that superantigens, as environmental factors, can change a controllable disease into one that becomes relentless for susceptible individuals. To illustrate the detrimental effects of superantigens on disease outcome, modulation of experimental allergic encephalomyelitis by superantigen, as well as the potential role of superantigens in human immunodeficiency virus pathogenesis will be discussed. The information presented may provide valuable insight into the role of superantigens in autoimmunity and human immunodeficiency virus infection.

Superantigens

Superantigens are potent modulators of the immune system. Some of their biological and immunological properties are reviewed here with special attention to their potential significance for cutaneous inflammation, specific skin immune responses and skin diseases.

The role of host immune responses in determining the outcome of HIV infection

The progression of disease following infection with human immunodeficiency virus (HIV) correlates with an activated immune system and would appear to depend to some degree on the immunogenetics of the host. Here, Michael Westby, Fabrizio Manca and Angus Dalgleish discuss the evidence for HLA determination of clinical outcome and the potential implications of a restricted T-cell receptor repertoire for pathogenesis.

HLA class II on HIV particles is functional in superantigen presentation to human T cells: implications for HIV pathogenesis

The mechanisms of immune suppression by the human immunodeficiency virus, HIV-1, are more complex than simple helper T cell deletion via infection and viral-induced lysis. Since the recent description of cellular proteins associated with HIV suggests that these proteins may be active in viral pathogenesis, the nature of HLA class II gene product carried on HIV, one of the most abundant of the human components carried with the virus, was examined. HIV bearing HLA-DR was shown to act with bacterial superantigen, staphylococcal enterotoxin A (SEA), to stimulate highly purified human T lymphocytes. T cell stimulation by wild-type HIV was shown by both induction of proliferation and by production of the cytokine interleukin 2 (IL-2). In contrast, HIV produced from mutant cells lacking class II genes were unable to cooperate with SEA to activate T cells. Neither whole HIV nor several proteins purified from HIV (gp120, gp41, p24, p7, and p6) exhibited superantigen-like activity in this system. HLA-DR-bearing HIV could, in the continued presence of SEA, induce T cell apoptosis, as detected by nuclear fragmentation and morphological criteria. These data indicate that human cellular proteins associated with HIV may be biologically active, and these proteins should be considered in mechanisms of viral pathogenicity and immunogenicity.

Rapid flow cytometric method for measuring lymphocyte subset activation

Standard in vitro methods for assessing T-cell activation have typically measured either the proliferative responses of peripheral blood mononuclear cell (PBMC) cultures to various provocative stimuli employing tritiated thymidine incorporation or the secretion of specific cytokines from activated cells. These bulk assay methods suffer the drawback of being lengthy assays, and, in addition, they do not provide information about functional responses of individual lymphocyte subsets. This report describes a three-color flow cytometric method for the rapid analysis (4 hours) of individual T-cell subsets in whole blood responding to various provocative stimuli, including pokeweed mitogen, the comitogenic monoclonal antibodies (mAbs) CD2/CD2R, the superantigen staphylococcal enterotoxin B (SEB), and the specific antigen Candida albicans. After 4 hours, CD69 expression in response to CD2/CD2R paralleled thymidine incorporation measured after 72 hours. Variations in the proportions of CD4+ and CD4- T cells expressing CD69 were observed with different stimuli. These observations demonstrate the potential of multiparameter flow cytometry for the investigation of functional responses of individual T-cell subsets to a variety of stimuli in whole blood.

Identification of three human sequences with viral superantigen-specific primers

The open reading frame (ORF) in the long terminal repeat (LTR) of mouse mammary tumor virus (MMTV) has recently been shown to encode multiple products including a negative acting factor (Naf) and a superantigen (Sag). Expression of superantigens from endogenous MMTV loci in the mouse results in the deletion of whole classes of T cells. In a PCR approach, with primers to the MMTV ORF and hybridization to MMTV specific probes, we have identified three human sequences. Direct sequencing of PCR products revealed that one of these products is related to a human autoantigen that is conserved among many species and is expressed in testes and sperm. The second sequence that we have identified is novel, and no evidence for expression of this sequence could be obtained. Finally, the third ORF-like sequence is a new member of a previously described family of human endogenous retroviruses (RTVL-I). This sequence is transcribed in several human cell lines, including B lymphoblastoid cells, and is thus the first demonstration that an RTVL-I-related sequence can be expressed. Taken together, these findings raise the intriguing possibility that the human genome contains superantigen-like sequences, some of which are also related to endogenous retroviruses, that may influence the T cell repertoire.

Multifactorial nature of human immunodeficiency virus disease: implications for therapy

The immunopathogenic mechanisms underlying human immunodeficiency virus (HIV) disease are extremely complex; the disease process is multifactorial with multiple overlapping phases. Viral burden is substantial and viral replication occurs throughout the entire course of HIV infection. Inappropriate immune activation and elevated secretion of certain cytokines compound the pathogenic process. Profound immunosuppression ultimately occurs together with a disruption of the microenvironment of the immune system, which is probably unable to regenerate spontaneously. Thus, therapeutic strategies in HIV disease must not be unidimensional, but rather must be linked to the complex pathogenic components of the disease and must address where feasible each of the recognized pathogenic processes for the possibility of therapeutic intervention.