Mouse Anti-Cat Fel d 1 monoclonal antibody for ELISA. Fel d 1 is a protein that in cats is encoded by the CH1 (chain 1/Fel d 1-A) and CH2 (chain 2/Fel d 1-B) genes. The protein is of an unknown function to the animal but causes an IgG or IgE reaction in sensitive humans (either as an allergic or asthmatic response).