Resistance and immune response in scabies-infested hosts immunized with Dermatophagoides mites

Seventy-one percent of rabbits immunized with a mixed (50:50) Dermatophagoides farinae and D. pteronyssinus house dust mite extract were resistant to infestation by Sarcoptes scabiei var. canis. The resistance was evidenced by a marked reduction in parasite load. All immunized hosts developed similar immunogen-specific antibody titers that were independent of the levels of scabies infestation that developed when the hosts were infested with scabies. Resistant hosts exhibited significantly lower scabies-specific immunoglobulin titers and produced antibody to fewer scabies antigens than did nonresistant hosts. All infested hosts (resistant and nonresistant) showed a cellular infiltrate in the scabietic lesions that was composed of neutrophils, plasma cells, macrophages, and mononuclear cells. Resistant hosts were characterized by fewer plasma cells in the infiltrate than were observed for non-resistant hosts. Resistant hosts exhibited a gradual increase in the number of infiltrating neutrophils, followed by a decrease that correlated with a decrease in the mite burden. Nonresistant hosts exhibited an early rapid increase, a decrease, and then a gradual increase in the concentration of neutrophils as the mite load increased. These results clearly showed that D. farinae/D. pteronyssinus antigens/epitopes can sensitize the hosts to scabies mites and induce protective immunity. The lower circulating antibody levels and generally stronger inflammatory cell-mediated response of resistant hosts compared with nonresistant hosts suggested that the mechanism by which immunization with Dermatophagoides mites induces immunity to scabies mites involved a down-regulated T helper cell type 2 (Th2) response with reduced antibody production but an up-regulated and stronger Th1 (inflammatory cell-mediated) response to scabies.