A phenotypical analysis carried out by two-colour flow cytometry showed that the proportion of circulating CD4+ T lymphocytes co-expressing the membrane-associated ectoenzyme dipeptidyl peptidase IV (CD26 antigen), a functional collagen receptor involved in T-cell triggering through its interaction with the CD45 protein tyrosine phosphatase, was significantly lower in 28 children with non-translocated trisomy 21 (Down's syndrome) (DS) than that calculated in the bloodstream of 27 age- and sex-matched healthy controls. Agonist anti-CD26 monoclonal antibodies (MoAbs), such as anti-1F7, not only modulate the surface expression of this molecule, but also enhance the proliferative activity of normal human T cells via the CD3- and CD2-mediated activation pathways. T-lymphocyte proliferation induced by antigen or polyclonal T-cell activators, including anti-CD3 or -CD2 MoAbs, is severely impaired in DS. Although the physiological ligand of CD26 surface structure is unknown, the fact that CD4+ T lymphocytes found in the blood of trisomic subjects are mostly CD26- (anti-1F7-) suggests that their faulty mitogenic response may be due to phenotypical and, perhaps, strictly correlated functional abnormalities.

It is now well established that the CD30 glycoprotein is a surface antigen expressed by activated T cells producing T-helper (Th)-2-type lymphokines. Mounting laboratory evidence, however, suggests that CD30 expression is not confined to a functionally restricted subset of T cells, but also identifies activated cells with a Th-1 and Th-0 pattern of cytokine secretion. CD30-bearing T lymphocytes release a soluble form of the molecule (sCD30), which can be detected both in vitro and in vivo. In the present study, very high levels of sCD30 were found in colostrum from 20 puerperal women, but not in autologous and heterologous (nonpregnant women) blood samples. These data strongly support an involvement of CD30+ T cells in the immune processes which take place at the level of the mammary gland during pregnancy and lactation. Passively transferred immune components such as immunoglobulins, cytokines, macrophages, natural killer cells, granulocytes and memory/activated T cells, all of which may help the baby to fight off infections, have been revealed in human breast milk. However, how Th-2-type cytokine-secreting T cells or other T-cell types help to endow the congenitally immunocompromised newborn infant with extrinsic immunological support remains an open question.

A phenotypical analysis carried out by direct immunofluorescence and two-colour cytofluorometry showed that the number of lymphocytes bearing the gamma delta T-cell receptor heterodimer was increased in the blood of eight children with Listeria monocytogenes infection, mainly due to an expansion of cells identified by monoclonal antibodies which recognize V delta 2 gene products. These findings are further evidence that gamma delta T cells are in some way involved in the immune response directed against human intracellular pathogens.

A strongly positive tuberculin skin reaction (> 1.5 cm2) was observed during the acute phase of the illness in 11 children with Kawasaki disease (KD), but not in control pediatric patients with other febrile infections (41 patients) or diseases similar to KD (9 patients). The cutaneous sensitivity to intermediate strength [5 tuberculin units (TU)] purified protein derivative (PPD) inoculation had completely disappeared by the second monthly checkup. Peripheral blood T lymphocytes from KD subjects proliferated vigorously and produced significant amounts of IL-2 in response to the stimulation elicited by 0.05 TU/mL of PPD. In contrast, the proliferative response of, and IL-2 release by, control T cells was within background values. Mounting laboratory evidence suggests that heat shock proteins (HSP) may be involved in the pathogenesis of KD. Our clinical and experimental data may, therefore, have been due to immunologic cross-reactivity between mycobacterial derived HSP65 and its human homologue HPS63 (self P1 antigen). Despite the low number of patients investigated, our findings suggest that the tuberculin skin test and its in vitro correlates (T cell mitogenesis and IL-2 production) could provide simple and reliable diagnostic tools for identifying atypical forms of KD, or vice versa, in subjects not vaccinated against tuberculosis.

The numerical and phenotypical differences in semen gamma delta T lymphocytes provide further evidence of a defined migrating lymphocyte subset balance in anatomically and physiologically distinct areas of the body. Their functional role, in terms of both helper and suppressor-cytotoxic activities in the nonsterile proximal portions of the male genital tract, now needs to be explored in detail.

The biological role of T cell receptor (TCR) gamma delta bearing cells is not yet fully understood. We studied 12 children with Bordetella pertussis infection and 12 age- and sex-matched healthy controls. Patients with whooping-cough yielded significantly lower relative and absolute numbers of blood TCR-gamma delta + cells than normal controls (both p < 0.001). It is suggested that the depletion of circulating gamma delta T cells in patients with Bordetella pertussis infection might be the result of the dispatch of these cells to the site of inflammation, i.e. the bronchial mucosa. Interestingly, other human lung diseases, such as allergic bronchial asthma and sarcoidosis display similar pulmonary phenotypical features.

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The expression levels of CD26 and CD31 surface antigens, two adhesion/activation molecules with helper and suppressor activities, respectively, were found to be significantly higher on human colostral T cells (CD3+) than in autologous peripheral blood samples. These findings provide further phenotypical evidence that immune system T lymphocytes are compartmentalized in the mammary gland late in pregnancy and during lactation. The question of whether these overexpanded T lymphocyte populations in breast milk modulate in situ, either by enhancing or suppressing, the cellular and/or humoral immune response of the suckling infant remains to be answered. Additional studies are, therefore, needed to explore this intriguing field concerning the immunology of the colostrum.