Final answer:
An R1r patient transfused with R2R2 blood can become sensitized and produce anti-E antibodies, potentially leading to a hemolytic transfusion reaction upon subsequent exposure.
Step-by-step explanation:
An R1r patient expressing the Rh CcEe antigens and lacking the Rh D antigen (r indicates the absence of the D antigen) transfused with R2R2 blood would be exposed to the E antigen. Assuming the patient has not been previously sensitized to the Rh antigens, an initial exposure would not typically result in an immediate reaction. However, the immune system can be sensitized to produce anti-E antibodies after this exposure and a subsequent transfusion with blood containing the E antigen could lead to a hemolytic transfusion reaction.
It's also important to note that Rh incompatibilities, unlike ABO incompatibilities, typically require a previous exposure for the immune system to produce anti-Rh antibodies. This is because whereas blood type antibodies (like anti-A or anti-B) are naturally occurring, anti-Rh antibodies (including anti-D, anti-C, anti-E, anti-c, and anti-e) require sensitization. When dealing with Rh factor, the most significant one is Rh D, which is indicated by the presence of the D antigen on the red blood cells; the lack of this antigen characterizes Rh- individuals.