In an Immunodiffusion Test to Diagnose the Fungal Disease Histoplasmosis

In an immunodiffusion test to diagnose the fungal disease histoplasmosis, a patientʹs serum is placed in a well in an agar plate. In a positive test, a precipitate forms as the serum diffuses from the well and meets material diffusing from a second well. In this test process, what is the most likely identity of the material in the second well?

A) red blood cells
B) a purified fungal antigen
C) a purified protozoan antigen
D) antibodies
E) entire fungal cells