Representative flow cytometric analysis of uninfected human <t>PBMC</t> (A) and <t>FIV-infected</t> feline (B) and human (C and D) PBMC. By using a monoclonal antibody specific to FIV p24 (clone 43-1B9), viral capsid protein was detected in 12% of Petaluma-infected human PBMC by flow cytometry (D) compared to 0.8 and 91.6% of cells in uninfected human PBMC (C) and FIV-infected feline PBMC (B) cultures, respectively. By using an isotype-matched control antibody, 2.4% of human PBMC were recognized (A).