Characterization and epitope identification of the T cell response in non-allergic individuals exposed to mouse allergen

Abstract

Background Exposure to airborne allergens is a frequent trigger of respiratory allergy and asthma in atopic individuals. While allergic patients suffer hypersensitivity reactions to these allergens, non-allergic individuals do not exhibit clinical symptoms despite environmental exposure to these ubiquitous allergen sources. The aim of this study was to characterize T cell responses in non-allergic laboratory workers, who are heavily exposed to mice allergens (Exposed Non-Allergics, ENA) and compare this data to previously published T cell responses measured in mouse (MO)-allergic patients. METHODS: Peripheral mononuclear cells (PBMC) from ENA subjects were expanded for 2 weeks in vitro with mouse urine extract and screened for IFNγ and IL-5 cytokine production in response to mouse antigen-derived peptides by ELISPOT. Ex vivo T cell reactivity in the ENA cohort was performed after 6hr stimulation with peptide pools by intracellular staining of CD154. Results Vigorous responses were detected, associated with 147 epitopes derived from 16 mouse antigens. As expected, responses in ENA subjects were somewhat lower than those observed in MO-allergics for both responder frequency and overall response magnitude. While responses in allergics were polarized towards IL-5 production and associated with low IFNγ production, ENA responses were not polarized. The composition of targeted antigens and epitopes was overall similar between the two cohorts, with the majority of T cell reactivity directed against Mus m 1 and other major urinary proteins. However, kappa-casein precursor and odorant binding protein Ib were more abundantly recognized in MO-allergics compared to ENA subjects. Additionally, T cell responses against oligopeptides derived from the low molecular weight fraction of mouse urine were also assessed. Interestingly, no difference in the response frequency, magnitude or polarization between MO-allergic and ENA individuals was observed. Finally, assessment of ex vivo T cell activation also revealed T cell reactivity in the ENA cohort, with a non-significant trend for lower responses compared to MO-allergics. Conclusion Exposure to mouse induces potent T cell responses in non-allergic individuals, targeting similar epitopes as seen in allergic patients.

B cells modulate mouse allergen-specific T cells in nonallergic laboratory animal-care workers

“…To confirm this observation in a larger group of subjects, and to exclude possible artifact introduced by in vitro culture, we used the activation-induced marker (AIM) assay. We and others previously demonstrated that allergen-specific T cells can be detectable ex vivo using this assay in combination with pools of T cell epitopes ( 12 – 14 ). This technique uses the upregulation of the activation markers 4-1BB (CD137) and OX40 (CD134) as a read-out for T cell reactivity and has been applied in previous studies ( 12 – 14 ) to quantify mouse allergen-specific T cells after HiMO peptide stimulation.…”

“…We and others previously demonstrated that allergen-specific T cells can be detectable ex vivo using this assay in combination with pools of T cell epitopes ( 12 – 14 ). This technique uses the upregulation of the activation markers 4-1BB (CD137) and OX40 (CD134) as a read-out for T cell reactivity and has been applied in previous studies ( 12 – 14 ) to quantify mouse allergen-specific T cells after HiMO peptide stimulation. Representative plots of the mouse allergen-specific T cell responses before reexposure and ARE, as measured by the AIM assay, which detects the fraction of activated CD4 T cells in response to antigen-specific stimulation by measuring the 4-1BB (CD137) and OX40 (CD134) cell markers are shown in Figure 1B .…”

“…More recently, reduced CD4 T cell responses after exposure to allergens has been reported in seasonal pollen allergy ( 9 ). Our group previously reported detectable CD4 T cell responses in ENA individuals ( 14 ) using developed peptide pools of mouse allergens ( 12 , 13 ). In the present study, similar downregulation of CD4 T cell responses was observed in mouse allergy among ENA laboratory animal-care workers ARE to mouse allergen, as evidenced by a decrease both in proportion of activated 4-1BB + OX40 + CD4 T cells and in IFN-γ and IL-5 cytokine production.…”

“…Previous work demonstrated that when reexposed to mouse allergens, ENA individuals have lower but still sizable CD4 T cell reactivity as well as absent polarization compared with an allergy group. Moreover, the protein targets of ENA reactivity are similar to those in symptomatic subjects ( 14 ). These observations prompt further investigation on additional differences in immune profiles between ENA and allergic individuals and whether the nonallergic status is a passive consequence or active response to mouse allergens.…”

“…Importantly, these subjects have lower but still sizable T cell reactivity after reexposure (ARE) of mouse allergens. However, compared with allergic subjects where the responses are polarized toward high IL-5 and low IFN-γ production, ENA subjects showed no polarization ( 14 ). The cause of the lack of polarization and the regulatory mechanisms in ENA subjects ARE to allergens are currently unknown.…”