From Th1 to Th2: diabetes immunotherapy shifts gears

Predisposition to atopic symptoms to inhaled antigens may protect from childhood type 1 diabetes

OBJECTIVE

To assess the inverse association between type 1 diabetes and asthma to establish whether environmental and/or genetic factors predisposing to asthma or to atopic symptoms to inhaled antigens protect from diabetes. RESEACH DESIGN AND METHODS: Questionnaires were returned by 306 probands with childhood type 1 diabetes, their 506 nonaffected siblings, and 406 age- and sex-matched unaffected population control subjects. The main outcome measures were self-reported physician-diagnosed asthma and atopic symptoms to animal dust and pollen.

RESULTS

Risk of diabetes was inversely associated with asthma (odds ratio 0.49 [95% CI 0.24-1.00]), allergy to animal dust (0.67 [0.45-0.99]), and to a lesser degree to pollen (0.74 [0.51-1.07]) when the probands were compared with the population control subjects. Among the children of the families of an affected proband, the risk of diabetes appeared to be inversely associated with asthma (0.54 [0.27-1.09]) but not with allergy to animal dust (0.99 [0.66-1.47]) nor allergy to pollen (0.88 [0.62-1.27]).

CONCLUSIONS

The frequency of asthma and atopic symptoms to some inhaled antigens is decreased in individuals with childhood type 1 diabetes. Factors predisposing to atopic symptoms to inhaled antigens may protect from childhood type 1 diabetes.

Decreased prevalence of atopic diseases in children with diabetes. The EURODIAB Substudy 2 Study Group

OBJECTIVE

To test the hypothesis that atopic diseases in early life are associated with a reduced risk (protection) for the development of type 1 diabetes in childhood.

STUDY DESIGN

European centers (n = 8) with access to population-based type 1 diabetes registries (>90% degree of ascertainment) participated in a case control study focusing on early exposures and risk factors for type 1 diabetes. Altogether, data from 1028 members of a case group and 2744 members of a control group corresponding to 85.4% eligible members of the case group and 76.1% of the control group were analyzed. Information in this study was collected regarding atopic diseases (atopic eczema, allergic rhinoconjunctivitis, and asthma).

RESULTS

Atopic disease and asthma particularly are associated with significant reductions in risk of childhood type 1 diabetes. The risk reduction associated with asthma was observed reasonably consistently among the 8 study centers, which represent a wide range of diabetes incidence. Risk reductions associated with all 3 expressions of atopy were particularly marked in children whose type 1 diabetes was diagnosed in the 10- to 14-year age group.

CONCLUSION

These findings indicate that atopic conditions may be protective against the development of type 1 diabetes and are consistent with the immunologic concept of T(H)1 (type 1 diabetes) and T(H)2 (atopy) diseases being mutually exclusive.

Shifting T-cell activation thresholds in autoimmunity and determinant spreading

The best-characterized autoimmune T-cell response is that to myelin basic protein (MBP). MBP has classically been regarded as a sequestered antigen that does not cause negative selection. This view has been fostered by the observation that T-cell receptor-transgenic T cells that are specific for the "immunodominant determinant" on the molecule, MBP:Ac1-11, persist as naive cells in MBP-expressing H-2u mice. The same T cells, however, can cause autoimmune pathology once they have been primed by environmental stimulation to become memory cells. Once the autoimmune response to Ac1-11 has been engaged, determinant spreading occurs and second-wave T-cell responses that are specific for weaker, "cryptic" determinants like MBP:121-140 develop. Although the nature of these cryptic determinants has been enigmatic, recent studies using MBP-/- mice have provided new insights. These studies showed that MBP is not a sequestered antigen, but one that causes negative selection; as MBP:121-140 is actually the immunodominant determinant in MBP-/- mice, it tolerizes high avidity clones in MBP+/+ mice, making it appear cryptic. Based on this new information, we attempt here to redefine the MBP-specific repertoire within the theoretical framework of the threshold model for negative selection, and we propose a model of shifting T-cell activation thresholds to explain how ignorant/naive T cells can become effector cells of autoimmune pathology and why this effector cell repertoire spreads.