Zymosan A enhances humoral immune responses to soluble protein in chickens

Vaccination is the most effective method for controlling the infectious diseases that threaten the poultry industry worldwide. The use of adjuvants or immunostimulants is often necessary to improve vaccine efficacy, particularly for vaccines based on recombinant protein or inactivated pathogens. The adjuvant effects of zymosan A on antigen-specific antibody production were investigated in chickens. First, the optimal adjuvant dose of zymosan A was determined. Chicks were immunized with dinitrophenyl-keyhole limpet hemocyanin (DNP-KLH) at a dosage of 2 mg/kg body weight (BW) with or without zymosan A (at a dosage of 0.5 mg/kg BW) co-administration at 4, 5 and 6 weeks of age. Different routes of immunization (oral, intranasal (i.n.), intraocular (i.o.), subcutaneous (s.c.), intramuscular (i.m.) and intraperitoneal (i.p.) were tested. Anti-DNP IgY and IgA concentrations in serum samples from all chicks were measured by an enzyme-linked immunosorbent assay. The results revealed that co-administration of zymosan A with DNP-KLH significantly increased anti-DNP IgY concentrations in chicks immunized by the oral and s.c. routes of administration when compared with control groups. In addition, co-administration of zymosan A with DNP-KLH significantly increased anti-DNP IgA concentrations in chicks immunized by the oral, i.o. and s.c. routes compared with control groups. In conclusion, zymosan A is a useful immune-potentiator adjuvant in chickens, and its co-administration with vaccine antigens enhances humoral immune responses.