DIGESTION OF HOST IMMUNOGLOBULIN AND ACTIVITY OF MIDGUT PROTEASES IN THE BUFFALO FLY HAEMATOBIA-IRRITANS EXIGUA

The digestion of blood by the buffalo fly (Haematobia irritans exigua) was monitored for 6 h at 33 degrees C after a single meal. Following the meal, the concentration of soluble protein within the mid,out incr eased to a peak at 2 hours then decreased steadily over the next 4 h. The magnitude of the increase in soluble protein at 2 h indicated a re lease of protein from another source most likely from lysed red blood cells. The immunoglobulin (IgG) fraction of the blood meal was digeste d rapidly (50% within one hour of feeding) and fully digested within 4 h. This is indicative of its accessibility to digestive enzymes withi n the midgut. In contrast, when flies had continuous access to blood, the concentration of IgG in the midgut remained at a more constant lev el. The loss of antigen-binding activity of a specific antibody was mo re rapid than complete degradation of the IgG, with 70% of binding act ivity lost within one hour of feeding. The level of trypsin activity i n the midgut increased from pre-feeding levels to reach a peak at 2 h before returning to basal levels after 6 h, The pattern of trypsin act ivity follows closely that of the concentration of soluble protein in the midgut (r = 0.88). The activity of leucine aminopeptidase in the m idgut also increased immediately after feeding and remained elevated f or 4 h before declining to a basal level after 6 h. The rapid digestio n of IgG and subsequent loss of antibody activity suggests that for a specific anti-buffalo fly antibody to be effective it would need to be able to either evade the digestive system or induce a rapid response. (C) 1998 Elsevier Science Ltd. All rights reserved.