Second the B-cell antigen receptor delivers the antigen to intracellular sites where it is degraded and returned to the B-cell surface as. First like the antigen receptor on T cells it transmits signals directly to the cells interior when it binds antigen see Section 6-1. Role Of Mrna In Protein Synthesis Video Lesson Transcript Study Com Innate immune systems are found in all animals. . Mitochondria and chloroplastsThe theory proposes that these organelles evolved from certain types of bacteria that eukaryotic cells engulfed through phagocytosisThese cells and the bacteria trapped inside them entered an endosymbiotic relationship meaning that the bacteria. The immune system protects its host from infection with layered defenses of increasing specificity. Symbiogenesis explains the origins of eukaryotes whose cells contain two major kinds of organelle. If a pathogen breaches these barriers the innate immune system provides