Plays an essential role in the innate immune response against bacteria, fungi and protozoa infection (PubMed:15006349, PubMed:23166497, PubMed:24039584, PubMed:25012124, PubMed:30690067). After proteolytic cleavage, the protein C-terminus binds covalently through a thioester bond to the pathogen surface resulting in pathogen clearance either by melanization or lysis (PubMed:24039584, PubMed:30690067). Initiate the recruitment and activation of a cascade of proteases, mostly of CLIP-domain serine proteases, which leads to the proteolytic cleavage of the prophenoloxidase (PPO) into active phenoloxidase (PO), the rate-limiting enzyme in melanin biosynthesis (PubMed:24039584, PubMed:25012124, PubMed:23166497). In response to parasite P.berghei-mediated infection, binds to and mediates killing of ookinetes, as they egress from midgut epithelial cells into the basal labyrinth, by both lysis and melanization (PubMed:15006349, PubMed:25012124, PubMed:24039584). During bacterial infection, binds to both Gram-positive and Gram-negative bacteria but only promotes phagocytosis of Gram-negative bacteria (PubMed:24039584, PubMed:30690067). Promotes the accumulation of SPCLIP1 onto the surface of P.berghei ookinetes and bacterium E.coli which leads to the melanization of the pathogen (PubMed:24039584). Recruits CLIPA2 to bacteria surface (PubMed:25012124). In response to bacterial infection, required for periostial hemocyte aggregation, but not for the aggregation of sessile hemocytes in non-periostial regions (PubMed:30690067). During the late stage of fungus B.bassiana-mediated infection, required for the initiation of hyphae melanization by binding to the surface of hyphae and recruiting prophenoloxidase PPO to them (PubMed:23166497). Plays a role in male fertility by binding to defective sperm cells and promoting their removal during spermatogenesis (By similarity). Binds to and mediates killing of parasite P.bergei ookinetes by lysis. Binds covalently through a thioester bond to the pathogen surface resulting in pathogen clearance. Heterodimer of a TEP1-N chain and an TEP1-C chain non-covalently linked (PubMed:19286136). Forms a complex composed of TEP1-N and TEP1-C heterodimer, LRIM1 and APL1C; the interaction stabilizes TEP1-N and TEP1-C heterodimer, prevents its binding to tissues while circulating in the hemolymph and protects the thioester bond from hydrolysis (PubMed:19286136). Mature TEP1 and to a lesser extent full-length TEP1 interact with SPCLIP1; the interaction is induced by microbial infection (PubMed:24039584). Secreted as a full-length protein into the hemolymph. By parasite P.berghei infection; expression picks 24 hours post infection and increases again 4 days post infection. In the hemolymph, the full-length protein is cleaved by an unknow protease into a 75kDa N-terminal (TEP1-N) chain and an 80kDa C-terminal (TEP1-C) chain which remain non-covalently linked (PubMed:15006349, PubMed:19286136, PubMed:24039584, PubMed:25012124). The TEP1-C chain contains the thioester bond which covalently binds to the pathogen surface (By similarity). Cleavage is induced by bacterial infection or aseptic wound injury (PubMed:24039584). During embryonic and pupal development, the cleaved form is the predominant form (By similarity). N-glycosylated. TEP1 gene is highly polymorphic mainly in the region surrounding the thioester bond (PubMed:19797663). After proteolytic cleavage, TEP1*S alleles are more susceptible to hydrolysis of the intramolecular thioester bond than TEP1*R alleles (PubMed:23055931). Two main alleles have been described, TEP1*S and TEP1*R (PubMed:19797663). TEP1*S1 allele (AC Q9GYW4, strain PEST) or TEP1*S3 allele (this entry, strain G3) confer susceptibility to parasite P. berghei infection while TEP1*R1 allele (AC C9XI66, strain L3-5) confers resistance to P.berghei infection (PubMed:19797663). Approximately 20% of parasites survive in TEP1*S mosquitos and melanization of ookinetes is less efficient (PubMed:19797663, PubMed:15006349). In TEP1*S mosquitos, dead parasites are disposed by lysis, while in TEP1*R mosquitoes are killed both via lysis and melanization (PubMed:15006349). In TEP1*S2 male mosquitos, removal of defective sperm is more efficient resulting in enhanced male fertility (PubMed:26394016). RNAi-mediated knockdown in females causes a 5-fold increase in the number of oocysts following infection with parasite P.berghei (PubMed:15006349, PubMed:25012124). Inhibits SPCLIP1 binding to P.berghei ookinete surface and to E.coli surface, cleavage of CLIPA8 in the hemolymph and causes a severe decrease in phenoloxidase (PO) activity (PubMed:24039584). In knockdown mosquitos infected with bacterium E.coli, survival is reduced, bacteria proliferation is increased and PO activation is severely reduced (PubMed:25012124). RNAi-mediated knockdown does not affect the number of periostial hemocytes in non-infected mosquitoes; however, reduces the aggregation of hemocytes at the periostial regions in E.coli-infected mosquitos (PubMed:30690067). No difference in the spatial distribution of periostial hemocytes or sessile hemocytes outside the periostial regions in absence or following E.coli infection (PubMed:30690067). Slower E.coli clearance and severe reduction in melanization at the periostial regions (PubMed:30690067). Increased sensitivity to fungus B.bassiana (strain 80.2) infection characterized by reduced mosquito survival and increased levels of hyphal body colonies (PubMed:23166497). Impaired melanization of hyphae, but not of germinating conidia or germ tubes, caused by a failure to recruit prophenoloxidase PPO to hyphae (PubMed:23166497). Loss of phenoloxidase (PO) activity triggered during late but not early fungal infection (PubMed:23166497).