Effects of whole blood lysis and fixation on the infectivity of human T-lymphotropic virus type 1 (HTLV-1)

Whole blood lysis and fixation methods for flow cytometric (FCM) analysis were tested for their ability to reduce the infectivity of human T-lymphotropic virus type 1 (HTLV-1). Our goals were to: (1) determine the effects of 1.0 and 2.0% paraformaldehyde (PF) fixation on HTLV-1 infected cell lines and (2) assess the infectivity of blood samples containing HTLV-1-infected cells following processing with 5 commercially available products (Immuno-lyse, ImmunoPrep/Q-Prep, FACS lysis solution, CenTrak lyse and fix reagent, and Ortho-mune lysing reagent) compared to ammonium chloride lysis with either 0.1 or 1.0% PF fixation. Infectivity was determined by monitoring HTLV-1 p24 antigen production in cocultures of treated leukocytes with uninfected peripheral blood mononuclear cells (PBMC). Each method effectively reduced the viability of treated leukocytes. Commercial lysis/fixation methods significantly reduced HTLV-1 infectivity compared to prepared ammonium chloride/PF-based methods. For all preparations, increasing the time of fixation (e.g., 60 min) effectively reduced viral infectivity. Taken together, these data suggest that commercially available fixatives greatly reduce, but do not eliminate the risk of HTLV-1 infection during processing of viral-infected cells for FCM analysis.