Western blot using Matrix Protein p15 polyclonal antibody (Cat # PAB10208) to detect p15 in the culture supernatant of FIV-infected feline CrFK cells (Lane 2, arrowhead). Lane 1 is an uninfected control. Virions were enriched by ultracentrifugation, lysed, resolved by electrophoresis, and transferred to nitrocellulose. The membrane was probed with the primary antibody at a 1:10,000 dilution. Personal Communication, B. Luttge, CCR-NCI, Frederick, MD.