Interaction of Ia antigen-bearing polymorphonuclear leukocytes and murine splenocytes

The regulatory roles of neutrophils in adaptive immunity

Neutrophils have long been considered as cells playing a crucial role in the immune defence against invading pathogens. Accumulating evidence strongly supported the direct and indirect regulatory effects of neutrophils on adaptive immunity. Exogenous cytokines or cytokines produced in an autocrine manner as well as a cell-to-cell contact between neutrophils and T cells could induce the expression of MHC-II and costimulatory molecules on neutrophils, supporting that neutrophils may function as antigen-presenting cells (APCs) in respects of presenting antigens and activating T cells. In addition to the inflammatory roles, neutrophils also have the propensity and ability to suppress the immune response through different mechanisms. In this review, we will mainly highlight the heterogeneity and functional plasticity of neutrophils and the antigen-presenting capacity of different neutrophil subsets. We also discuss mechanisms relevant to the regulatory effects of neutrophils on adaptive immunity. Understanding how neutrophils modulate adaptive immunity may provide novel strategies and new therapeutic approaches for diseases associated with neutrophils.

Modulation of the antibody response to the HIV envelope subunit by co-administration of infectious or heat-inactivated canarypoxvirus (ALVAC) preparations

Poxviruses are large DNA viruses capable of infecting a broad range of animal species. Infection is generally accompanied by an inflammatory response in the host, the extent of which varies considerably with the specific poxvirus and host species. Regarding ALVAC, a poxvirus derived from the canarypox vaccine strain, Kanapox, and which represents a promising immunization vehicle in humans, nothing is known about its inflammatory capacity. The present study was aimed at documenting this issue in rodents, including mice and guinea pigs. It was then attempted to evaluate how such properties could influence the immunogenicity of an antigen concomitantly administered with ALVAC preparations using the HIV envelope subunit, rgp160, as the model immunogen. The results revealed that ALVAC, either infectious or heat-inactivated, induced in both animal species an early inflammatory response, as evidenced by a rapid migration of neutrophils to the site of inoculation. In parallel, the canarypoxvirus was shown to strongly adjuvant the co-administered immunogen, resulting in a marked increase in Env-specific IgG, IgG1 and particularly IgG2(a) serum titers. Of further interest, the heat-inactivated preparation of ALVAC retained this immunostimulatory activity. Whether or not a link between the inflammatory and immunomodulatory properties of ALVAC exists remains to be established, but such features are clearly interesting with respect to the potential use of ALVAC as an immunization vehicle.

Polymorphonuclear leukocyte regulation of lymphocyte proliferation and differentiation

The polymorphonuclear neutrophil (PMN) regulates in vivo and in vitro immune responses. We report that the immunoenhancing properties of PMN culture supernatants from PMN recruited by the bacterium Actinomyces viscosus (AV) show its exclusive effects on the T cell lymphocyte population. A study of the effect of PMN supernatants on normal Balb/c splenocytes to T and B cell mitogens showed enhancing effects on T cell mitogens, but no effect on B cell mitogen responses when compared to a control. Adherent cells (macrophages) were not required for the enhancing effect, indicating that the supernatant worked directly on the T cell. Proliferation of El-4, a Lyt-1.2 positive lymphoma helper cell, was directly affected by these supernatants. Functionally, T cell-dependent plaque-forming cell responses to sheep red blood cells (SRBC) were enhanced. The polyclonal, T cell-independent plaque-forming cell response was unaffected when generated with LPS as assayed with Protein-A-SRBC. These results indicate that PMN supernatants from cells recruited by AV act on a helper T cell population to enhance both proliferation and differentiation in lymphocyte populations. These interactions provide insight into local inflammatory responses of PMN-lymphocyte infiltration with altered cell-mediated immunity.