CD4+ and CD8+ alpha/beta+ T cells of the T helper cell (Th)2 phenotype produce the cytokines IL-4, IL-5, and IL-13 that promote IgE production and eosinophilic inflammation. IL-4 may play an important role in mediating the differentiation of antigenically naive alpha/beta+ T cells into Th2 cells. Murine NK1.1+ (CD4+ or CD4-CD8-) alpha/beta+ T cells comprise a beta 2-microglobulin (beta 2m)-dependent cell population that rapidly produces IL-4 after cell activation in vitro and in vivo and has been proposed as a source of IL-4 for Th2 cell differentiation. alpha/beta+ CD8+ T cells, most of which require beta 2m for their development, have also been proposed as positive regulators of allergen-induced Th2 responses. We tested whether beta 2m-dependent T cells were essential for Th2 cell-mediated allergic reactions by treating wild-type, beta 2m-deficient (beta 2m -/-), and IL-4-deficient (IL-4 -/-) mice of the C57BL/6 genetic background with ovalbumin (OVA), using a protocol that induces robust allergic pulmonary disease in wild-type mice. OVA-treated beta 2m -/- mice had circulating levels of total and OVA-specific IgE, pulmonary eosinophilia, and expression of IL-4, IL-5, and IL-13 mRNA in bronchial lymph node tissue similar to that of OVA-treated wild-type mice. In contrast, these responses in OVA-treated IL-4 -/- mice were all either undetectable or markedly reduced compared with wild-type mice, confirming that IL-4 was required in this allergic model. These results indicate that the NK1.1+ alpha/beta+ T cell population, as well as other beta 2m-dependent populations, such as most peripheral alpha/beta+ CD8+ T cells, are dispensable for the Th2 pulmonary response to protein allergens.

Inhalation of antigen in immunized mice induces an infiltration of eosinophils into the airways and increased bronchial hyperreactivity as are observed in human asthma. We employed a model of late-phase allergic pulmonary inflammation in mice to address the role of leukotrienes (LT) in mediating airway eosinophilia and hyperreactivity to methacholine. Allergen intranasal challenge in OVA-sensitized mice induced LTB4 and LTC4 release into the airspace, widespread mucus occlusion of the airways, leukocytic infiltration of the airway tissue and broncho-alveolar lavage fluid that was predominantly eosinophils, and bronchial hyperreactivity to methacholine. Specific inhibitors of 5-lipoxygenase and 5-lipoxygenase-activating protein (FLAP) blocked airway mucus release and infiltration by eosinophils indicating a key role for leukotrienes in these features of allergic pulmonary inflammation. The role of leukotrienes or eosinophils in mediating airway hyperresponsiveness to aeroallergen could not be established, however, in this murine model.

In the mouse and human, mRNA transcripts encoding the lymphocyte-specific protein tyrosine kinase p56lck are derived from two separate promoters resulting in heterogeneity in the 5' untranslated region sequence. The proximal promoter lies just 5' to the coding region for the gene and is active only in thymocytes. In contrast, the distal promoter lies 34 kilobases (kb) 5' in the human, and is active both in thymocytes and mature peripheral T cells. As previously reported, transgenic mice bearing functional proximal promoter sequence juxtaposed with the SV40 large T antigen gene invariably develop lymphoid tumors confined to the thymus. In the current work, transgenic mice bearing a 2.6-kb fragment of the human distal promoter fused to the SV40 large T antigen gene express large T antigen in thymocytes and in peripheral lymphoid cells, and develop tumors of both the thymus and the peripheral lymphoid organs. The ability of the human distal promoter to function appropriately in transgenic mice is consistent with the strong similarity observed between the mouse and human distal promoter sequences. With the exception of a single short interval that serves as a target for binding of nuclear factors, significant sequence similarity is not seen when the distal and proximal promoter sequences are compared. Hence, developmentally regulated, lineage-specific transcription of the lck gene is mediated by distinct promoter sequences that appear to be capable of functioning independently.

Using a transgenic mouse model we show that increased intrathymic expression of interleukin 4 (IL-4) significantly perturbs the development of thymocytes. Transgenic double-positive (CD4+CD8+) thymocytes, which are present in dramatically reduced numbers, exhibit increased T cell receptor (TCR) expression and increased mobilization of calcium mediated by these receptors. In contrast, transgenic single-positive (CD4+CD8- and CD4-CD8+) thymocytes and peripheral T cells exhibit decreased TCR-mediated calcium mobilization. The development of CD4-CD8+ thymocytes is significantly perturbed by IL-4 expressed in vivo; only peripheral CD4+ T cells are found in significant numbers in transgenic mice, while CD4-CD8+ thymocytes are present in increased numbers, apparently because of their failure to emigrate to the periphery. In contrast to these selective effects on T cell development, no significant differences in the numbers of B cells or mast cells, or in the plasma levels of IgE and IgG1 are observed between transgenic and control mice. These observations suggest that IL-4 in vivo exerts its major effects locally rather than systemically, even when its expression is constitutively increased.

IFN-gamma mRNA levels in human neonatal blood mononuclear cells or highly purified T cells were markedly lower than those of adult cells after incubation with Con A and PMA. In contrast, IL-2, IL-2-R, and T3 delta chain mRNA levels were kinetically and quantitatively similar in neonatal and adult T cells. The peak amount of IFN-gamma and IL-2 mRNA correlated well with IFN-gamma and IL-2 detected in supernatants of both neonatal and adult T cells. These results suggest that reduced IFN-gamma mRNA levels in neonatal T cells is due to an intrinsic deficiency at the pretranslational level and indicate that the magnitude of IL-2 and IFN-gamma gene expression can be independently modulated pretranslationally.