Pneumocystis jiroveci (also P. carinii) is a fungal organism which is detected in human tissues (typically in lung in immunocompromised patients) in the trophozoite stage. It is the causative organism of Pneumocystis pneumonia. This antibody reacts with an epitope on the organism which is resistant to formalin, picric acid, paraffin, alchohol, and xylene. No cross-reactivity occurs with other fungi or parasitic organisms.