There are two variants of the receptor, each encoded by a separate gene:
CD120a - TNFR1 - TNFR superfamily member 1A
CD120b - TNFR2 - TNFR superfamily member 1B
TNFR1 is the receptor type responsible for mediation of TNF-alpha induced sickness behavior, and is involved in neurotoxic processes. Elevated levels of TNFR1 has been found in severe mental disorders.