Effect of reinfestations on systemic immune responses in cattle naturally infested by Hypoderma sp. (Diptera: Oestridae).

Systemic humoral and cellular immune responses were studied during natural infestations by Hypoderma lineatum in cattle at their first (G-1) and second exposure (G-2). Four out of seven animals in G-1 were palpation positive, with a mean intensity of 11.2 (12.81SD) warbles; the same proportion (4/7) presented warbles in G-2 but the intensity was 3.7 (2.21SD). The evolution of total IgG levels was characterized by a noticeable increment coinciding with the presence of warbles on the back, especially in G-2. The IgG1 isotype displayed a parallel evolution in both groups, with peak values prior to the appearance of first warbles. The IgG2 subclass followed an irregular pattern in both groups and IgM maintained low and constant levels throughout the study, mainly in G-1. CD4/CD8 ratios showed a predominance of CD4(+) throughout the infestation, principally in G-2 during the warble season. The evolution of IFN-γ in G-2 was constant, whereas in G-1 there was a gradual descent until warble emergence. The dynamics of the IL-10 differed between G-1 and G-2, although both groups showed a significant drop after the exit of the larvae that could be implicated in the termination of the inflammatory response. IL-4 and TNF-α levels did not show differences between groups. Our results suggest that the resistance mechanisms would become more apparent at the latest stages of the infestation by Hypoderma, supporting the hypothesis that considerable larval destruction in sensitized animals might take place after their arrival to the back.