Comparison of Fel d 1 and Fel d 4 levels in house dust samples from the Canadian CHILD birth cohort.

RATIONALE: The cat lipocalin allergen, Fel d 4, elicits IgE responses in ~60% of cat-allergic patients and is also reported to induce pro-inflammatory Th2 responses. Feld4 is considered the second most important allergen after Feld1. Environmental exposure to Feld4 has not previously been investigated. The aim was to compare exposure to Feld1 and Feld4 in dust samples from homes to assess dual exposures.

METHODS: The Canadian Healthy Infant Longitudinal Development (CHILD) cohort study enrolled 3500 children and collected a dust sample at age 3 months from each participant home. A subset of 97 settled dust samples were screened for Feld1 by MARIA and for Feld4 by ELISA. The lower limit of detection (LLOD) was 0.004µg/g and 0.008µg/g for Feld1 and Feld4, respectively.

RESULTS: All 97 dust extracts were positive for Feld1 and many contained exceptionally high allergen levels (range 0.007-1,822µg/g). Approximately 65% were positive for Feld4, however, the allergen levels were ~100-fold lower than Feld1 (range <0.008-21µg/g). Although samples with high Feld4 also contained high Feld1, there was a poor quantitative correlation between the two allergen exposures (R²=0.12).

CONCLUSIONS: Both Feld1 and Feld4 are prevalent in household dust, though Feld1 provides the better assessment of cat exposure. The Feld4 levels are within a range that would be expected to cause sensitization and this may be important in cat allergic patients showing minimum reaction to Feld1.