Antibody responses following immunotherapy with cat pelt extract

IgG antibody responses to a major allergen, cat allergen 1 (cat 1), and to a minimally allergenic protein, cat albumin (alb), were studied in patients who had received 4 to 11 mo of immunotherapy with three concentrations of crude cat pelt extract. A double-antibody radioimmunoassay utilizing 125I-labeled antigen was used to measure IgG and IgE antibody. The high-dose group (HDG)(n = 5), which was composed of the active-treatment group of a previously reported double-blind study, received a mean cumulative dose of 3440 microgram cat 1 and 10,660 microgram alb. The intermediate-dose group (IDG) (n = 6) and low -dose group (IDG)(n = 5) received 70 and 0.930 microgram of cat 1 and 217 and 2.86 microgram of alb. IgE antibody to cat 1 before treatment was measurable in most patients. IgE antibody to alb was either no measurable or of a low level. Mean (geometric) before-and-after IgG levels (U/ml) to cat 1 in the HDG, IDG, and LDG were 420 and 7794, 158 and 1388, an 191 and 1365, respectively. Mean before-and-after IgG levels (U/ml) to alb in the HDG, IDG, and LDG were 72 and 348, 1.9 and 4584, and 0.4 and 508, respectively. Two patients (HDG) had no IgG antibody to alb after treatment. Another patient (HDG) had 82,364 U/ml IgG antibody to alb and precipitating antibody by gel diffusion. Very intense IgG antibody response to both cat 1 and alb were seen over a wide range of immunizing doses.