Th2 T cell priming can occur in the lung in the absence of APC migration to draining lymph nodes. (a) Groups of C57BL/6 and LTα knockout mice were given a subcutaneous delivery of L. major promastigotes in the right hind foot, and at weekly intervals their right and left footpad thickness was measured using spring-loaded calipers. Plot shows the mean ratio ± SE (n = 10) of infected to uninfected foot measurements in C57BL/6 (WT) versus lymph node–deficient (KO) mice. (b) Groups of C57BL/6 and LTα knockout mice, with or without splenectomy, were given an intranasal administration of L. major parasites and challenged 7 days later with a second intranasal dose of parasites to induce effector responses. Four days after challenge, the mice were sacrificed and their BAL cells recovered, followed by perfusion with PBS and isolation of lung tissue. Bar graph shows the mean (± SE) proportions of lymphocytes (LYMPHs), neutrophils (NEUTs), and eosinophils (EOs) recovered from BAL of individual WT, LTα knockout (KO), and splenectomized LTα knockout (KO + SP^–) mice (n = 5 per group). Macrophages make up the remaining percentage of cells recovered by BAL and have been omitted for clarity. (c) Lung tissue cells from mice in b were isolated by collagenase/DNase treatment and set up in culture with varying doses of L. major–soluble lysate and splenic APCs to induce antigen-specific cytokine production. Bar graphs show the mean IFN-γ, IL-5, and IL-13 production of duplicate ELISA wells after 4 days of culture.