Signals that regulate the host response to Mycobacterium tuberculosis.

An appropriate T helper (Th) 1 immune response is required for the elimination of Mycobacterium tuberculosis. The factors regulating the polarization of mouse or human T cells to produce Th1 or Th2 cytokines are briefly reviewed. These factors include host genetics, cytokines present at the site of T cell activation, the type, dose and localization of antigen, the type of antigen-presenting cells, the engagement of different costimulatory molecules, steroid hormones and age. T cells of children produce low levels of gamma-interferon and we hypothesize that this may partly explain the differences in the clinical manifestations of tuberculosis in children and adults. Given that Th2 cytokines inhibit Th1 responses, the question arises of whether individuals mounting prominent Th2 responses, manifested by high serum IgE levels, are more susceptible to M. tuberculosis. In a community with a high incidence of tuberculosis, serum IgF levels, a marker of prominent Th2 responses, correlate with disease incidence and with socioeconomic deprivation. We propose that Th2 immune dominance, probably induced by intestinal parasites, enhances susceptibility to tuberculosis. Furthermore, our finding that serum IgE declines in patients following active tuberculosis argues that tuberculosis down-regulates Th2 responses.

In situ production of gamma interferon, interleukin-4, and tumor necrosis factor alpha mRNA in human lung tuberculous granulomas.

Human tuberculous granulomas from five adults undergoing surgery for hemoptysis were analyzed by nonradioactive in situ hybridization for tumor necrosis factor alpha (TNF-alpha), gamma interferon (IFN-gamma), and interleukin-4 (IL-4) gene expression. All of the patients produced TNF-alpha mRNA. Three patients stained positive for both IFN-gamma and IL-4 mRNA; the other two stained positive for IFN-gamma but not IL-4 mRNA. Heterogeneity between the granulomas was observed in those patients staining positive for both IFN-gamma and IL-4 mRNA; these patients exhibited granulomas having IFN-gamma and not IL-4 mRNA as well as granulomas positive for both cytokine mRNAs. There was no evidence of caseation in these granulomas, and the cytokine patterns may represent events in the evolution of the granuloma. However, in those granulomas exhibiting caseous necrosis, very little IFN-gamma or IL-4 mRNA was observed, implying that progression of the granuloma is accompanied by a down regulation of T-cell responses. TNF-alpha mRNA expression was highest in patients with both IFN-gamma and IL-4 mRNA. Populations of CD68 positive macrophage-like cells within the granulomas produce mRNA for TNF-alpha, IFN-gamma, and IL-4. This implies that macrophages within the tuberculous granuloma may not be dependent on T-cell cytokines for modulation of their function but may be able to regulate their own activation state and that of the surrounding T cells. These findings have implications on the delivery of immunotherapies to patients with tuberculosis.

Baboon CYP11B1: the localization and catalytic activity in baboon adrenal tissue.

A third gene encoding baboon CYP11B1 was isolated and was shown to catalyze only the metabolism of deoxycorticosterone (DOC) to corticosterone. The investigation into the localization of CYP11B1 in the baboon adrenal tissue, using in situ hybridization, showed that mRNA transcripts were predominantly present in the zona reticularis (ZR) and zona fasciculata (ZF). Signal was also observed in the zona glomerulosa (ZG) and scattered within the medulla. Immunohistochemical studies, using rabbit anti-sheep CYP11B1 IgG, indicated that CYP11B1 was expressed only in the zona fasciculata, zona reticularis and in the medulla. CYP11B1 was not detected in the zona glomerulosa. Subsequent Western Blot investigations into the presence of CYP11B1 in baboon adrenal cortex and medullary homogenates indicated CYP11B1 as a single band in the cortex and as two distinct bands in the medulla. CYP11A was present only in the baboon adrenal cortex. The metabolism of deoxycorticosterone and corticosterone was subsequently investigated in the baboon adrenal cortex and medulla. In cortex homogenates, deoxycorticosterone was converted to corticosterone, and neither 18-hydroxycorticosterone nor aldosterone was detected. In medulla homogenates, however, corticosterone was metabolized to aldosterone, as confirmed by APcI-MS.

Breast tumour cell-induced down-regulation of type I collagen mRNA in fibroblasts.

This study investigated the modulation of type I collagen gene expression in normal fibroblasts by breast tumour cells. Northern analysis of total RNA extracted from stages I, II and III breast tumour tissue revealed that collagen mRNA levels were elevated in stage I tumours compared to the adjacent normal breast tissues, whereas they were decreased in stages II and III breast tumours. This aberrant collagen gene expression was confirmed by non-radioactive RNA:RNA in situ hybridization analysis of 30 breast carcinomas which localized the production of type I collagen mRNA to the stromal fibroblasts within the vicinity of the tumour cells. In order to determine whether the tumour cells were directly responsible for this altered collagen production by the adjacent fibroblasts, breast tumour cell lines were co-cultured with normal fibroblasts for in vitro assessment of collagen and steady-state collagen RNA levels. Co-culture of tumour cells and normal fibroblasts in the same dish resulted in down-regulation of collagen mRNA and protein. Treatment of the fibroblasts with tumour-cell conditioned medium also resulted in decreased collagen protein levels but the mRNA levels, however, remained unaltered. These results suggested that the tumour cells either secrete a labile 'factor', or express a cell surface protein requiring direct contact with the fibroblasts, resulting in down-regulation of collagen gene expression. Modulation of the ECM is a common characteristic of invading tumour cells and usually involves increased production of collagenases by the tumour cells or stromal fibroblasts. This study showed that tumour cells were also able to modulate collagen mRNA production by stromal fibroblasts, which may facilitate tumour cell invasion and metastasis.