This page needs more information about how C4a is an isomorph of C4 and how this part of the complement system is related to HLA. https://en.wikipedia.org/wiki/Complement_component_4
human leukocyte antigen complex (HLA) - A set of genes responsible for a given person's immune response to potential threats. Specifically, HLA genes encode proteins which help the immune system to distinguish the body's own proteins from proteins which are made by foreign invaders like bacteria and viruses. The HLA complex can vary greatly from person to person, generating unique immune and allergic responses. (Learn more: mecfsresearchreview.me)
