FIG. 6.

Effect of lymphocyte depletion on the isotype of FMDV-specific antibody responses. Examples of the FMDV-specific antibody isotype profiles are displayed for an anti-CD4 MAb-treated animal (a) and for a TRT3 control MAb-treated animal (b) from experiment 2. ▵, IgG1; □, IgG2; ⧫, IgM. The CD4⁺ cell population was depleted from the lymphoid tissue of experiment 2 anti-CD4 MAb-treated animals on study day 5 postinfection, and circulating CD4⁺ lymphocytes were depleted from anti-CD4 MAb-treated animals in both experiments up to at least 7 days postinfection (9 days postinfection for animal VT74). Efficient antibody isotype class switching occurred during the period of CD4⁺ T-cell depletion.