Changes in cat specific IgE and IgG antibodies with decreased cat exposure.

Background: Current understanding of the effects of reducing exposure to cat allergens is limited. It has also become clear that there are different forms of immune response to cat allergens.

Objective: To investigate changes in skin tests and cat specific IgG and IgE antibodies when students from a home with a cat move to a college dormitory.

Methods: Ninety-seven college students participated in a prospective study that consisted of allergy skin prick testing and serum measurement of IgE and IgG antibodies to cat at the beginning and end of one academic year in college. A subgroup returned for follow-up at the end of 2 years.

Results: Among 97 students, 33% had IgG antibodies to Fel d 1 but no evidence of sensitization, 25% had positive skin test results and/or serum IgE antibodies, and 42% had negative skin test results and no detectable serum antibodies. Among the non-cat sensitized students with IgG antibodies, the titers decreased during 8 months (P = .002). Titers of IgG4 to Fel d 1 also decreased (P < .001). Among the sensitized students, no change in IgE antibodies to cat occurred in 8 months (P = .20), whereas Fel d 1 specific IgG antibodies decreased (P < .001). Thus, ratios of IgG to IgE decreased highly significantly (P = .007). Among the students with negative skin test results who returned for follow-up (n = 56), none developed positive skin test results or serum IgE antibodies.

Conclusion: Under conditions of marked decrease in exposure, no participants developed new-onset sensitization. Among the individuals sensitized at study entry, there were major decreases in the ratio of IgG to IgE.