Ethnic origin, genetics, gender and environmental factors have been shown to influence some immunologic indices, so that development of reference values for populations of different backgrounds may be necessary. We have determined the distribution of lymphocyte subsets in healthy Brazilian individuals from birth to adulthood. Lymphocyte subsets were determined using four-colour cytometry in a cross-sectional study of 463 human immunodeficiency virus-unexposed children and adults from birth through 49 years of age. Lymphocyte subsets varied according to age, as previously observed in other studies. However, total CD4+ T cell numbers were lower than what was described in the Pediatric AIDS Clinical Trials Group P1009 (PACTG P1009), which assessed an American population of predominantly African and Hispanic backgrounds until the 12-18 year age range, when values were comparable. Naïve percentages and absolute values of CD8+ T cells, as assessed by CD45RA expression, were also lower than the PACTG P1009 data for all analysed age ranges. CD38 expression on both CD4+ and CD8+ T cells was lower than the PACTG P1009 values, with a widening gap between the two studies at older age ranges. Different patterns of cell differentiation seem to occur in different settings and may have characteristic expression within each population.

IPEX is a rare X‐linked syndrome, with immune dysfunction, polyendocrinopathy and enteropathy. We describe an infant who died at the age of 11 months after developing eczema, severe diarrhoea, diabetes, hypothyroidism, thrombocytopenia and four episodes of septicaemia. Immunophenotyping of peripheral blood at 8 months revealed normal CD3+ T, CD4+ T and CD8+ T cell numbers, with low NK and B cells. CD4+ and CD8+ T lymphocytes showed remarkably low numbers and percentages of naïve cells and high numbers of memory CD4 and CD8 cells. At autopsy, an intense depletion of immune cells in thymus, spleen and lymph nodes was observed. No Hassall’s corpuscles were found in thymus. Lymphocytic pancreatitis and intense villous atrophy with mucosal lymphocytic infiltration in small bowel were also seen. FOXP3 gene studies revealed a: C→G substitution 3 bp upstream of exon 10, which prevents splicing between exons 9 and 10, likely resulting in a functionally altered or deficient protein. Florid clinical findings are usually observed in association of forkhead DNA‐binding domain mutations. The intense depletion of naïve T cells we report suggest that depletion of immune cells might take place due to uncontrolled activation due to the absence of regulatory T cells.

Diagnosis of primary immunodeficiency diseases (PID), based on laboratory tests and assessment of T lymphocyte function, is crucial in patients who present with lymphopenia. We evaluated T lymphocyte function in healthy children and adults and in patients and with PID using flow cytometry. Whole blood cultures were stimulated with phytohemagglutinin, purified protein derivate (PPD) and candidin, followed by detection of intracellular interferon-gamma (IFN - gamma) and CD25 membrane expression on CD3+ T cells by flow cytometry. Flow cytometry results were compared with 3H-thymidine (3HTdR) lymproliferation after in vitro cell stimulation and with delayed type hypersensitivity reaction (DTH). Patients with PID had lower intracellular IFN - gamma production than healthy children and healthy adults after PHA stimulation for 18 h (p = 0.024 and p < 0.0001, respectively); CD25 expression was also lower in patients with PID than in healthy children and adults after candidin stimulation (p = 0.048 and p < 0.0001, respectively). CD25 expression after PPD and candidin stimulation were also higher in healthy adults when compared with both patients and with healthy children (p < 0.0001 for all comparisons). Lymphoproliferation assay with 3HTdR after candidin stimulation did not show any significant difference between healthy children and patients with PID, but the response was higher in healthy adults (p = 0.029). The DTH for PPD was not different between PID and healthy children (p = 0.281). Intracellular IFN-gamma after PHA stimulation for 18 h and CD25 membrane expression after candidin stimulation for 72 h on CD3+ T cells were most reliable parameters that could discriminate PID patients from healthy children. Our results confirm the high variability in functional cell assays and reinforce the idea that age differences must be taken into consideration during assay evaluation.