Inhalant allergen‐specific T‐cell reactivity is detectable in close to 100% of atopic and normal individuals: covert responses are unmasked by serum‐free medium

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Abstract
Background It is widely held that in vitro T cell responses to allergens are more prominent in atopic than in normal individuals, though this conclusion is based upon culture techniques which fail to detect proliferative responses in a significant minority of atopies and many normals. Objectives: Study allergen‐specific proliferative responses of T cells cultured in serum‐free medium (SFM). Examine associations between atopic status, age and T cell reactivity. Methods Initially, peripheral blood mononuclear cells were stimulated with allergens or antigens in SFM, and compared with cells cultured in RPMI + 10% fetal calf serum or human AB serum. Subsequently, T cell reactivity was studied in 34 adults (20–49 years), 27 children (2–13 years), and 19 infants (≤ 10 weeks) using SFM alone. Results Compared with serum‐supplemented medium, SFM enhanced net T cell proliferation, both in bulk culture and when cloning at limiting dilution. In many subjects, SFM unmasked T cell reactivity to allergens which was not otherwise evident, and lowered the threshold allergen levels required for in vitro T cell triggering. For most allergens, T cell proliferative responses did not differ between adults who had specific IgE, and those who did not. The most vigorous responses observed were to ubiquitous inhalant allergens, which stimulated T cells from close to 100% of adults and children, and over 60% of infants. In contrast, responses to the ‘vaccine’ antigen tetanus toxoid were completely absent in the latter age group, but present in the majority of adults and children. Conclusions These findings suggest that the extent of active T cell recognition of environmental allergens has been hitherto underestimated, and further that these responses may frequently be initiated in very early life. Additionally, these findings reinforce the notion that qualitative (as opposed to quantitative) variations in specific T cell reactivity ultimately determine allergen responder phenotype.

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