Localized complement activation in the development of protective immunity against Ostertagia ostertagi infections in cattle

The gastrointestinal nematode Ostertagia ostertagi is one of major causal agents that contribute to production inefficiency in cattle industry in the temperate region of the world. One of pathophysiological factors that lead to reduced weight gain and milk yield is altered gastrointestinal functions, resulting from considerable tissue damage in the abomasal mucosa during infections. Protective immunity to Ostertagia ostertagi infections in cattle develops very slowly. Resistance to reinfection becomes manifest only after a prolonged period of exposure. Mechanisms underlying the development of protective immunity remain largely unexplored. Immune animals, with significantly reduced worm burdens, were developed after multiple drug-attenuated experimental infections and were compared to the primary infected group and their respective uninfected controls. In this study, transcriptomic analysis identified 3 signaling pathways, the complement system, leukocyte extravasation and acute phase responses, significantly impacted during both primary and repeat infections. The markedly increased mRNA levels of complement components C3, factor B (CFB), and factor I (CFI) in the abomasal mucosa of the infected cattle were confirmed using quantitative PCR. Western blot analysis established the presence of elevated levels of activated C3 proteins in the mucosa. One of the iniators of local complement activation could be related with secretory IgA and IgM because infections significantly upregulated expression of J chain (IGJ) as well as polymeric Ig receptor (PIGR) and an IgM-specific receptor (FAIM3), suggesting sustained increase in both synthesis and transepithelial transport of IgA and IgM during the infection. The elevated levels of pro-inflammatory cytokines, such as IL-4 and IL-1β, during the infection may be involved in gene regulation of complement components. Our data suggested enhanced tissue repair and mucin secretion in immune animals may also contribute to protective immunity. Our results presented the first piece of evidence that local complement activation may be involved in the development of long term protective immunity and provided a novel mechanistic insight into resistance against Ostertagia ostertagi in cattle. Overall design: There were four treatment groups: naive control (never infected), primary infection, drug-attenuated control, and drug-attenuated 5th reinfection. Each group had 4 biolgical replicates. A total of 16 arrays were used for this experiment. The 2 major contrast were 1). The primary infection vs naive control; and 2). The drug-attenuated 5th reinfection vs the drug-attenuated control.