Alison H. Rose

Genetic ‘risk’ for atopy is associated with delayed postnatal maturation of T‐cell competence

Recent in vitro studies suggest that IgE production in adults is co‐ordinately regulated by negative signals from γIFN‐producing CD4+ T‐helper‐1 (TH‐1) and positive signals from IL‐4 producing (TH‐2) T‐cells. Additionally, seroepidemiological evidence has pinpointed infancy as the period of maximum lifetime risk for T‐cell sensitization to ubiquitous environmental antigens. The present study sought to elucidate the relationship between these observations, by examination of CD4+ T‐cell function in normal children and those genetically at‘high risk’ for atopy, spanning the age range (up to 4 years) in which IgE responses to environmental allergens is typically manifest. Immunocompetent T‐cell precursor frequencies (determined by cloning at limiting dilution) were markedly reduced in ‘high risk’ children relative to normals (0.53.0.29 vs 0.26.0.19; P= 0.0025). Consistent with reports from other laboratories employing bulk T‐cell culture techniques, the γIFN producing capacity of CD4+ T‐cell clones from both groups of children were markedly reduced relative to adults, and was lowest in the high risk group (P<0.02). IL‐4 production by CD4+ T‐cell clones from the normal children was within the adult range, but again was significantly lower in the high risk group (P<0.00005). This indicates that initial immune responses to environmental allergens in early childhood occur against a background of maturational ‘deficiency’ in CD4+ T‐cell function, and suggests the possibility that variations in the rate of postnatal maturation of T‐cell competence may be a contributing factor in the development of differing patterns of immunological responsiveness to environmental allergens.

An analysis of the relationship between γδ T cell receptor V gene usage and non-major histocompatibility complex-restricted cytotoxicity

γδ T cells are capable of mediating non‐major histocompatibility complex (MHC) restricted lysis of a variety of tumour cell lines. The mechanism of this lysis and its significance in tumour immunity are not clear. We have used a panel of five malignant mesothelioma (MM) cell lines, as well as standard tumour targets K562 and Daudi, to investigate some of the factors which could be involved in non‐MHC restricted cytotoxicity mediated by γδ T cells. Individual MM ceil lines, representing a panel of lines derived from a single cell type, varied in their susceptibility to lysis by γδ T cell clones. Individual γδ T cell clones also showed unique cytotoxic profiles, and differed in their cytotoxic potential. T cell receptor (TCR) γδ gene usage correlated with the ability of clones to lyse Daudi or K562; clones lysing Daudi expressing Vγ9 and clones lysing K562 expressing VγI subgroup genes. No strict correlation between Vγ and Vδ gene usage and MM reactivity was, however, demonstrable. There was also no correlation between yδ T cell lysis of MM cell lines and the capacity of γδ T cells to produce interferon‐γ, tumour necrosis factor‐α, interleukin‐2 or interleukin‐4, nor with their expression of CD8.

Asbestos-Induced Release of a Human Alveolar Macrophage-Derived Neutrophil Chemotactic Factor

Neutrophils accumulate in the alveoli of asbestos-exposed individuals. In determining whether asbestos fibers induce the release of neutrophil chemotactic factor (NCF) from human alveolar macrophages, alveolar macrophages (10(6) cell/mL) obtained by bronchoalveolar lavage from six non-asbestos-exposed control subjects were exposed to crocidolite (0.1 and 1 mg/mL), chrysotile (1 mg/mL), or medium alone for 4 h, and NCF activity was measured in the supernatants in a 48-well microchemotaxis chamber with polycarbonate membrane filters (pore size, 3 microns) and purified human neutrophils. Alveolar macrophages in medium alone released negligible amounts of NCF (4 +/- 1 neutrophils per high-power field [N/HPF]). When macrophages were exposed to crocidolite (0.1 and 1 mg/mL), significant NCF release occurred (43 +/- 9 and 105 +/- 32 N/HPF, respectively; p less than 0.01 for each amount compare to alveolar macrophages cultured in medium alone). Chrysotile (1 mg/mL) induced similar NCF release (96 +/- 14 N/HPF; p less than 0.01 compared to unstimulated alveolar macrophages). Partial characterization of the NCF by Sephadex G-25 fine gel filtration demonstrated a molecular size of less than 1,000 daltons. These results show that human alveolar macrophages release NCF after exposure to asbestos. Release of NCF by alveolar macrophages in asbestos-exposed individuals may play a central role in the pathogenesis of asbestosis.

IgE responses of malnourished mice: Immunogenic and tolerogenic effects of low-grade antigenic stimulation

Mice maintained on protein-restricted diets after weaning manifested normal IgE (and IgG) responses following intraperitoneal immunization under conditions of maximal antigenic stimulation, i.e., antigen adsorbed to adjuvant. However, antigenic challenge at levels closer to the stimulation threshold, employing soluble antigen alone, revealed marked differences between the immune competence of normal and malnourished animals. Diminished IgE responsiveness to soluble antigen in the malnourished mice was accompanied by enhanced susceptibility to the induction of antigen-specific tolerance associated with the appearance of suppressor T cells in the spleen. It is argued that enhanced susceptibility to suppressor T-cell induction under conditions of minimal antigenic stimulation may underlie the diminished IgE responsiveness of the malnourished animals.

Effect of a Low Protein Diet on IgE Antibody Responses in Balb/c Mice

Mice maintained on a low protein diet (4% casein initiated at weaning) produced IgE antibody responses to both ovalbumin and Ascaris body fluid proteins. The titres in young mice were comparable to those of mice maintained on a normal (20% protein) diet particularly at high doses of immunogen. However, following immunization with low doses of immunogen the initiation of antibody response in malnourished mice was delayed and the levels finally obtained were significantly suppressed below normal levels. This effect was more apparent in animals maintained for prolonged periods on diet. Possible mechanisms for this suppression are presented.

Effect of a low protein diet on the capacity of mice to express a type I hypersensitivity response.

The capacity of Balb/c mice maintained since weaning on a 4% protein diet to express in vivo immediate (type 1) hypersensitivity reactions was compared to that of age-matched animals maintained on a normal (18%) protein diet. The deprived mice had a lower total cellular population and lower mast cell numbers in their peritoneal cavity. However, the mean cellular histamine content was comparable between the two groups. The skin responses of malnourished mice to the histamine liberator 48/80 were depressed but both groups reacted equally to passive cutaneous anaphylaxis when sensitized with serum from immunized mice. These studies indicate that protein deprivation has not inhibited the capacity to synthesize physiologically active amines or to impair the biochemical pathway of amine release from mast cells.