Background High serum levels of cat‐specific IgG and IgG4 are associated with protection against allergic sensitization to cat, but whether this association applies to other animal allergens remains unclear.

Objective To determine if high levels of mouse‐specific IgG and IgG4 are associated with a decreased risk of mouse skin test sensitivity.

Methods Two hundred and sixty workers of a mouse facility underwent skin prick testing and completed a questionnaire. Serum levels of mouse‐specific IgG and IgG4 were quantified by solid‐phase antigen binding assays. Room air samples were collected and airborne Mus m 1 was quantified by ELISA.

Results Forty‐nine participants had a positive skin prick test to mouse. Mouse‐specific IgG was detected in 219 (84%) participants and IgG4 was detected in 72 (28%) participants. A detectable mouse‐specific IgG4 level was associated with an increased risk of mouse skin test sensitivity (odds ratios (OR) 6.4, 95% confidence intervals (CI) 3.3–12.4). Mouse‐specific IgG and IgG4 were both positively correlated with mouse allergen exposure (r_s=0.31, P=0.0001, and r_s=0.27, P=0.0006, respectively). The odds of skin test sensitivity peaked at moderate levels of IgG4, but decreased at the highest levels of mouse‐specific IgG4. In contrast, the odds of skin test sensitivity increased monotonically with IgG levels.

Conclusions A detectable level of mouse‐specific IgG4 is associated with an increased risk of skin test sensitivity to mouse. However, the highest IgG4 levels appear to be associated with an attenuated risk of mouse skin test sensitivity, suggesting that induction of high levels of IgG4 through natural exposure may protect against the development of allergic sensitization.