Hyalomma anatolicum anatolicum: the role of humoral factors in the acquisition of host resistance

A significant degree of resistance to Hyalomma anatolicum anatolicum can be adoptively transferred to naive recipients with immune serum from rabbits repeatedly infected with adult H. a. anatolicum. Ticks fed on recipients of immune serum took longer to become engorged and showed a significant decrease (P less than 0.01) in engorgement weight and oviposition compared with ticks that fed on recipients of normal serum. A direct correlation between resistance and anti-saliva IgG antibodies was indicated by a progressive increase in the degree of resistance and IgG antibody titres following successive tick infestations. Challenge feeding sites on actively sensitised hosts and recipients of immune serum revealed significantly greater infiltration of basophils and eosinophils compared with feeding sites on recipients of normal serum. However, both the degree of resistance and the accompanying cutaneous basophil and eosinophil responses in recipients of immune serum were considerably weaker than those induced by active tick feeding, thus suggesting that nonhumoral (cell-mediated) mechanisms might also be involved in acquired host resistance to H. a. anatolicum.