Host immune responsiveness to the chigger, Eutrombicula cinnabaris

Area of Science:

• Immunology
• Dermatology
• Parasitology

Background:

• Chigger bites (Eutrombicula cinnabaris) commonly cause skin reactions.
• The immune response to repeated chigger infestations is not fully understood.

Purpose of the Study:

• To investigate the development of cutaneous hypersensitivity to E. cinnabaris after repeated infestations in mice.
• To elucidate the immunological mechanisms underlying chigger bite reactions.

Main Methods:

• Mice underwent four E. cinnabaris infestations, separated by 14-day intervals.
• Macroscopic skin changes, cellular infiltrates, and immunological responses (adoptive transfer, skin testing) were assessed.
• Reactions were evaluated after initial and subsequent infestations.

Main Results:

• First infestation caused no visible reaction; subsequent infestations led to progressively severe erythema, epidermal thickening, and exudation.
• Third and fourth infestations induced significant cellular infiltrates, notably eosinophils.
• Adoptive transfer with lymphocytes and passive serum transfer demonstrated cell-mediated immunity and heightened reactivity.
• Skin tests indicated Arthus and delayed-type hypersensitivity responses to chigger antigens.

Conclusions:

• Repeated E. cinnabaris exposure induces a robust, cell-mediated cutaneous hypersensitivity.
• Eosinophils play a crucial role in the inflammatory response to chigger bites.
• Cellular immunity, mediated by lymphocytes, is primarily responsible for enhanced reactions to subsequent chigger infestations.