The C blood group antigens are specific proteins found on the surface of red blood cells. They are part of the Rh blood group system, which includes several other antigens, such as D and E. The presence or absence of these antigens can affect blood transfusions and pregnancy, as they can trigger immune responses in individuals with different blood types. Individuals with the C antigen are classified as either C positive or C negative, depending on whether they express this antigen. Understanding these antigens is crucial for safe blood transfusions and managing conditions like hemolytic disease of the newborn, where maternal antibodies may attack fetal red blood cells.