Leukocyte filtration was performed with HTLV-I-infected blood and with blood supplemented with cultured HTLV-I-transformed cells. Reduction of infectivity upon leukocyte filtration was determined by the polymerase chain reaction (PCR) using primers indicative for the HTLV-I-pol and tax genes. Two different commercially available filters were used: a column-shaped cellulose acetate and a flat-bed polyester filter. Both filters yielded reduction of at least 3 10logs for cultured HTLV-I-infected cells. When blood from HTLV-I-infected individuals was used for filtration, the number of infected cells was reduced by 1-3 10logs. Although filtered blood as yet cannot be regarded as safe, it is concluded that leukocyte filtration of HTLV-I-infected blood potentially contributes to reducing the spread of HTLV-I by blood transfusion.

A flow cytometric method for the detection of low amounts of lymphocytes, monocytes, and granulocytes in filtered red cells (RBCs) was evaluated. In this procedure, the RBCs in the samples were lysed by ammonium chloride treatment and the white cells (WBCs) were detected by flow cytometry according to their specific light-scattering properties. The identity of the WBC subpopulations was confirmed by immunofluorescence with monoclonal antibodies specific for each cell type. Flow cytometric determination of WBCs in filtered RBCs correlated with numbers obtained by both a hemocytometer (r = 0.76) and a radioimmunoassay (r = 0.79). Total numbers of WBCs in RBCs measured by flow cytometry were 59 +/- 13 percent (n = 7) of those measured by electronic particle counting, 32 +/- 6 percent (n = 25) by hemocytometer, and 48 +/- 11 percent (n = 29) by radioimmunoassay. Lymphocytes added to filtered RBCs in a concentration of 1.37 cells per microL were detected at an average of 0.56 +/- 0.22 cells per microL (n = 3). Results with monoclonal antibodies indicated an altered expression of membrane markers on granulocytes after RBC filtration, as seen with cell activation. The inefficiency of the flow cytometric method to detect the total number of WBCs calculated by other methods may reflect filtration-induced changes in light-scattering properties of the WBCs. Although the method described does not accurately quantitate the total numbers of WBCs present in filtered RBCs, it may provide useful information on qualitative aspects of WBC subpopulations.

The frequency of human T-cell lymphotropic virus types I and II (HTLV-I/II) polymerase chain reaction (PCR) reactivity was studied in two groups of high-risk individuals in Amsterdam: hard drug users and heterosexual outpatients of the sexual transmitted diseases (STD) clinic. Both groups were seronegative as determined by enzyme-linked immunosorbent assay (ELISA), Western blot (WB), and radioimmuno-precipitation assay (RIPA). Detection of HTLV-I and HTLV-II in peripheral blood mononuclear cells (MNC) was performed by PCR, using primer sets indicative for the pol and tax genes. In the hard drug users group (n = 25) no evidence of HTLV-I/II infection was found whereas in the STD group (n = 21) one individual was identified with HTLV-II proviral DNA. Positive reactions in PCR were confirmed only for three seropositive controls after in vitro culture of MNC but not for the PCR-positive, seronegative individual. Virus production in vitro could not be detected by a sensitive HTLV-I antigen capture assay for viral p24gag proteins after in vitro T-cell stimulation of MNC, either from PCR-positive or PCR-seronegative individuals. This suggests again a low viral production rate. It is concluded that infection with HTLV-II can be detected among high-risk seronegative individuals.