In vitro assessment of the feline cell-mediated immune response against feline panleukopeniavirus, calicivirus and felid herpesvirus 1 using 5-bromo-2′-deoxyuridine labeling

In this study an in vitro assay was optimized to detect feline proliferating lymphocytes as an assessment for the cell-mediated immune response. For this purpose, 5-bromo-2′-deoxyuridine (BrdU) labeling was chosen because of its sensitivity and the possibility of further characterization of proliferating cells. The assay was optimized by selecting the best batch and concentration of fetal bovine serum, β-mercaptoethanol concentration, cell density, BrdU incubation time and antigen presenting cell type. Cats were vaccinated with the attenuated Nobivac vaccine Tricat and the peripheral blood lymphocyte proliferation responses were quantified upon in vitro restimulation with inactivated and infectious feline panleukopenia virus (FPV), feline calicivirus (FCV) and felid herpesvirus 1 (FeHV-1). Proliferation signals were detected with inactivated FeHV-1 in the CD8+ but not in the CD8− T lymphocyte population, with inactivated FCV and FPV in both CD8− and CD8+ T lymphocyte populations. Restimulation with infectious FCV caused significant proliferation in the CD8− T lymphocyte population only while infectious FPV and FeHV-1 seemed to suppress lymphocyte proliferation in both T cell populations. Additional IFN-γ quantification in the culture supernatant revealed a large correlation between the proliferation signals and IFN-γ production, indicating that BrdU labeling is a very reliable technique to assess and characterize feline lymphoproliferative responses to viral antigens in vitro.