Nancy E. Street

The role of CD4+ and CD8+ T cells in the protective inflammatory response to a pulmonary cryptococcal infection

Moderately virulent strains of Cryptococcusneoformans, inoculated via the trachea, cause a pulmonary infection in BALB/c mice that was gradually resolved by T lymphocyte‐dependent mechanisms. The current studies, using monoclonal antibodies to deplete T cell subsets, demonstrated that CD4+ and CD8+ T cells combined to mediate a prominent pulmonary inflammatory infiltrate that included lymphocytes, macrophages, neutrophils, and eosinophils. The inflammatory response peaked 2 weeks after infection and coincided with the beginning of gradual pulmonary clearance of the infection. CD4/CD8 double, deficiency (4‐8‐) markedly reduced the influx of all cells into the lungs. A CD4 deficiency had a more profound effect on the total number of inflammatory cells recruited to the lungs than a CD8 deficiency. Depletion of either CD8+ or CD4+ T cells significantly decreased pulmonary macrophages and neutrophils, but only a CD4 deficiency prevented the influx of eosinophils. Recruitment of CD8+ T cells occurred independently of CD4+ T cells, but CD4+ T cell recruitment to the lungs was significantly reduced in CD8‐deficient mice. Mitogen‐stimulated infiltrating lung lymphocytes from infected 4+8+ mice secreted both T helper cell type 1 (Th1) [interferon‐γ (IFN‐γ) and interleukin‐2 (IL‐2)] and Th2 (IL‐4, IL‐5, and IL‐10) cytokines. CD4 deficiency resulted in loss of T cells secreting IL‐4, IL‐5, and IL‐10. However, residual CD8+ T cells still secreted IL‐2 and IFN‐γ. Lung T cells from CD8‐deficient mice secreted similar levels of IL‐4, IL‐5, and IL‐10 on a per lung basis compared with 4+8+ mice despite decreased numbers of CD4+ T cells, but secreted reduced levels of IFN‐γ. These experiments indicate that (1) CD4+ T cells play a dominant role in recruiting macrophages and granulocytes to the lung and (2) CD8+ T cells also mediate cellular recruitment, increase the magnitude of CD4+ T cell numbers in the infiltrate, and contribute to the local secretion of IFN‐γ. Thus, these studies demonstrate that CD8+ T cells can independently mediate an inflammatory response to a large, particulate, extracellular antigen, a role heretofore attributed almost solely to CD4+ T cells. J. Leukoc. Biol. 55: 35–42; 1994.

Induction of B cell tumor dormancy by anti-idiotypic antibodies

Long-term dormancy of murine B-cell lymphomas can be experimentally induced by immunizing the host with the idiotype expressed on the tumor. Interaction of the cells with anti-idiotype antibodies is sufficient to induce and maintain the dormant state. The growth of lymphoma cells interacting with anti-idiotype antibodies is arrested and they undergo dramatic changes in their morphology, cell-cycle status and oncogene expression. Regrowth of a tumor after long-term dormancy results from the emergence of a tumor cell variant that no longer responds to the antibodies with growth inhibition. These data demonstrate the feasibility of reversing a malignant phenotype of cells by specific growth arrest signals and suggest new approaches for therapeutic intervention in cancer.

CONTROL OF THE PRODUCTION OF SOLUBLE INTERLEUKIN-4 RECEPTORS : IMPLICATIONS IN IMMUNOREGULATION

Soluble cytokine receptors (sCR) are generated in vivo through proteolytic cleavage of the membrane‐bound receptors or by direct translation of mRNAs specifically encoding the soluble forms. Despite their widespread presence in biological fluids, the physiological role of endogenous sCR as immunoregulatory molecules is not yet well understood. In vivo, exogenous soluble interleukin‐4 receptors (sIL‐4R) have been shown to have both agonistic and antagonistic effects on IL‐4 responses, depending on the relative concentration ratios of sIL‐4R to IL‐4. In an effort to elucidate the potential role of endogenous sIL‐4R in the regulation of IL‐4 responses, the mechanisms controlling the production of sIL‐4R have been investigated. Although many cell types are able to constitutively produce low levels, production of sIL‐4R is significantly up‐regulated in vitro by T cell activation and IL‐4. The ability of splenic cells to produce sIL‐4R and the serum levels of sIL‐4R have consistently been found to be increased during immune responses characterized by T cell activation and IL‐4 secretion (Th2 responses). In agreement, clones of Th2, but not Th1, cells were found to significantly up‐regulate sIL‐4R production following antigenic stimulation. However, the production of sIL‐4R by Th2 cells appears to be independent from that of IL‐4 and can also be induced by cell contact and/or IL‐1‐dependent pathways. Taken together, these observations suggest that the production of sIL‐4R in vivo is closely associated with the secretion of IL‐4, and are consistent with the notion that endogenous sIL‐4R are involved in the regulation of IL‐4 activity during immune responses.

A synthetic standard DNA construct for use in quantification of murine cytokine mRNA molecules

A synthetic DNA construct has been developed as a standard molecule whereby murine cytokine mRNA molecules can be quantified by the reverse transcription-polymerase chain reaction (RT-PCR). The construct, designated Cytoquant 1, allows the quantification of murine IL-1 alpha, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10, IFN-gamma, TNF-alpha, TGF-beta, GM-CSF, CD4, CD8, HPRT and beta-actin mRNA levels. This technique is based on the amplification of a transcribed RNA molecule from Cytoquant 1 as an internal standard control in both the RT and PCR reactions. The quantification data from these analyses are expressed in absolute values, i.e. molecules/cell, which allows the data derived from separate experiments to be compared. In this study, mRNAs encoding beta-actin, IL-10, IFN-gamma and GM-CSF have been quantitated in both Th1 and Th2 cell clones with, and without, stimulation. The quantitative analysis data are highly reproducible and cytokine mRNA concentrations are reflective of restricted cytokine secretion patterns. Furthermore, constitutive cytokine mRNA levels are detectable in resting cells, eliminating the need for exogenous stimulation. The high degree of sensitivity and accuracy make this methodology uniquely suited for the study of T-cell subset cytokine expression in both in vivo and in vitro biological models.

Role of Antibody Signaling in Inducing Tumor Dormancy

Cancer dormancy is a well-recognized clinical phenomenon in which tumor cells are present, but the tumor burden does not increase for long periods of time1–3. However, tumor cells can regrow many years later. In breast cancer, there is a steady rate of recurrence 10 to 20 years after removal of the primary tumorl3,4 and the recurrent tumor frequently grows at a rapid rate(5). A particularly pertinent example is the low grade (follicular) form of non-Hodgkin’s lymphoma (NHL) in which long-term remissions are common but, eventually, virtually all die of a recurrence. Levy and Miller(5) have treated such patients with monoclonal anti-idiotype (Id) and have achieved remissions in a high proportion of patients. Relapses, many caused by Id-negative variants, are frequent indicating that the antibody (Ab) was particularly effective in inducing dormancy in cells bearing the corresponding idiotope but that hypermutation of VH and VL genes eventually allow some tumor cells from the original clone to escape(5–7).

The future of graduate and postdoctoral training in the biosciences

This article summarizes the outcomes of the second national conference on the Future of Bioscience Graduate and Postdoctoral Training. Five topics were addressed during the conference: diversity in leadership positions; mentoring; modernizing the curriculum; experiential learning; and the need for better data on trainees. The goal of the conference was to develop a consensus around these five topics and to recommend policies that can be implemented by academic and research institutions and federal funding agencies in the United States.