Interactions of murine leukemia virus (MuLV) with isolated lymphocytes. II. Infection of B and T cells with friend virus complex in diffusion chambers and in vitro: Effect of polyclonal mitogens

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Abstract
The infection of isolated B and T cells by a murine leukemia virus (Friend) (MuLV‐F) was studied both in vitro and in vitro with an implanted diffusion chamber system. Lymphocytes were obtained from pools of normal spleen cells by filtration of the cell suspension through a nylon‐wool column. The purity for both Ig positive and theta‐positive cells varied between 85% and 90% in the B‐cell and T‐cell fractions; both lymphocyte fractions responded very well to stimulation with their respective specific polyclonal mitogens, bacterial lipopolysaccharide (LPS) and concanavalin A (Con A). Lymphocytes were infected by incubating pelleted cells in 2–6 × 104 FFU MuLV for 1 h at 4°C and were then cultured for 5–10 days. Cells releasing infectious MuLV were enumerated as infectious centers (IC). IC were readily detectable in the cultures of infected B‐cells but none were found in the T‐cell cultures. Addition of LPS to the culture medium increased the number of IC in B‐cell fractions up to 1,000‐fold. Furthermore, in T‐cell cultures with LPS, IC also appeared in numbers which approximately correlated with the contaminating Ig+ cells of the T‐cell fraction. In contrast, Con A had no consistent effect on the infection of either B or T cells. In the absence of MuLV‐F, mitogenic stimulation alone did not elicit any endogenous IC. In subsequent experiments, purified lymphocytes were infected in diffusion chambers in vivo. The number of IC in infected B cells increased 1,000‐fold as compared to infection in tissue culture. The peak of infection at 10 days was followed by a slight decline. Infected cells were also found in diffusion chambers containing T‐cell fractions; these IC had very similar kinetics to those in B‐cell‐containing chambers, but their number was 10 times lower, suggesting that the infected cells were B cells, which comprised about 10% of the T‐cell fraction. The virus‐related antigens were detectable by immunofluorescence on the membrane of cells recovered from B‐cell‐bearing chambers but not on cells from T‐cell‐bearing chambers.