Chronic infections with Toxoplasma gondii occur in the brain of mammalian hosts. The understanding of the relationship between Toxoplasma gondii, CNS, and the immune system assists in comprehending how Toxoplasma affects the complement system and how it exerts a defense mechanism against Toxoplasma. This review focuses on the supervision of the complement system by Toxoplasma gondii during neural infections. There are three possible mechanisms by which the protozoan can invade the brain. Tachyzoites in bloodstreams multiply, invade, and bind to endothelial cells before migrating into parenchymas via transcellular crossing mechanisms. Secondly, the immune cells become like the Trojan horse, which carries intracellular parasites across the blood–brain barrier (BBB). In the third mechanical process, the BBB can directly be crossed through the brain at the tight junction (TJ) by the tachyzoites. It is concluded that C3 manipulation of the integrity of the BBB can be used to increase T.gondii invasion into the CNS..

The purpose of the current experiment was to test the immunization against Coenurus cerebralis in sheep. Sixteen animals (6 months old, from 1 October 2020 to 30 March 2021 in Najaf city) were recruited to perform the experiment, in which eight of them were injected twice at 21-day interval using the cellular metabolic antigen of C. cerebralis protoscolex cultivated and then emulsified by complete Freund's adjuvant (CFA). The shots were injected intramuscularly at a dose of 1 ml (15 mg of antigenic protein determined in a separate experiment). The second group of eight sheep served as controls (injected intramuscularly with 1 ml sterile saline only at the days of injections). Blood samples were collected from all animals at day-0 (before injection) and at day 10, 18, and 24 after the first injection, and at day10, 16,26, 40, 48, 53, 61, 80, 85, and 89 after the second injection. Serum activity was studied by indirect enzyme-linked immunosorbent assay (iELISA). The findings, by iELISA, revealed that the cellular antigen of C. cerebralis protoscolices is an active stimulator of antibody response. Day-10 (after the first injection) showed significantly (P<0.05) 3.4 to 9.9 time-higher antibody levels compared to those from day-0. This elevation in the titer of antibodies was increased after receiving the second dose showing 6.3 to 12 time-higher antibody presence even at the final days of blood collection compared to those from day-0. No changes were noticed in the sera of the control animals. The obtained data allow us to conclude that metabolites synthesized by cultivation are active immunogenic components that activate the humoral part of the immune system manifested by the increases in the antibody titers. This gives a solid ground for future work regarding alternative methods of discovering immunization techniques against cestodes.