Effect of hyposensitization upon the immediate and late asthmatic reaction and upon histamine reactivity in patients allergic to house dust mite (Dermatophagoides pteronyssinus).

The effect of hyposensitization (HS) upon the allergen evoked immediate asthmatic reaction (IAR), late asthmatic reaction (LAR) and upon bronchial reactivity towards histamine was examined. Eighteen young asthmatic patients were studied using a double-blind, placebo-controlled design. All were allergic to house dust mite (HDM) and demonstrated an IAR and a LAR after bronchial provocation with HDM. Furthermore, all, except one child, demonstrated bronchial hyperreactivity towards histamine (median provocative dose producing a 20% fall in forced expiratory volume in one second (PD20) histamine = 0.19 mg.ml-1, range: 0.02-8 mg.ml-1). The subjects were randomly divided into two groups to receive HDM or placebo injections during one year. After the one year period, the IAR was less severe in the subjects who received HDM injections (p = 0.02), while this reduction was not observed in the subjects who received placebo injections. Also, in the HDM group a small but significant increase of the median PD20 HDM was observed (p = 0.04). Furthermore, the LAR was less severe in the subjects who received HDM injections (p = 0.02), while the subjects who received placebo injections showed the same severity of LAR after one year (p = 0.44). Histamine reactivity did not change after HDM injections or after placebo injections. Thus, HS reduces the severity of the IAR and LAR without any change in histamine reactivity.