CTL responses are normal in CD44^−/− mice. (A) CD44^+/− (closed triangles) and CD44^−/− (open triangles) mice were infected IV with VSV (2 × 10⁶ pfu). VSV-infected syngeneic (EL-4) cells were labeled with ⁵¹Cr-label and used as targets. Closed circles represent noninfected control CD44^+/+ mice. Specific lysis of noninfected control targets less than 5%; spontaneous lysis of all targets less than 25%. (B-D) Secondary restimulation against VSV is normal in CD^−/− mice. Splenocytes from mice immunized with VSV (2 × 10⁶ pfu) on day 40 (B) or 80 (C and D) were restimulated with VSV nuclear protein class-1–binding peptide for 5 days in the absence (B and C) or presence (D) of ConA supernatant. Specific cytotoxicity against VSV-infected EL-4 (H-2^b) target cells was comparable with heterozygous control mice. Specific lysis of noninfected EL-4 cells is indicated by closed circles and was below 10% for all effector cells used. Spontaneous release was below 20% for both targets.