Difference between antigens, recognition & attachment proteinsWatch
What do you mean by "cellular communication" and also where are antigens made then if not the host cell? For example what makes the antigens on a body cell then? And exactly what is the use of antigens?
Recognition proteins are different. It's more along the lines of immune cells saying "Hey, this guy is one ours! We don't need to kill it!" This is part of the basis of the ABO blood typing system via MHC surface markers.
Antigens are primarily produced by non-self cells. Using the ABO example: Patient 1 is O negative (negative refers to the Rhesus factor). A blood transfusion from Patient 2 (expression of type A markers on cells) is put into Patient 1. Since Patient 1 normally does not have type A markers, the blood from Patient 2 immediately stimulates an immune response in Patient 1.
Another example would be lipopolysaccharide (LPS) expressed by gram negative bacteria. It isn't normally produced by the human body, thereby inducing an immune response.
Didn't you mention that cellar communication was enabled by recognition proteins?
From an immunology/cell biology point of view:
Recognition proteins are for identifying self/non-self.
Receptor proteins are for cellular communication/uptake of ions.
It is possible that A level terminology may have changed since I last covered these topics, but I doubt that is the case.