Nonsecretory antibody, but not CD4- or CD8-positive T cells, limits Hib colonization. (A) Individual depletion of either CD4- or CD8-positive cells does not affect colonization. The density of Hib PC+ in the upper respiratory tract lavage fluid of BALB/c mice treated with no antibody (control), MAb GK1.5 (anti-CD4), or MAb 2.43 (anti-CD8) to deplete CD4- or CD8-expressing cells, respectively, at 3 days p.i. (B) Nonsecretory antibody limits Hib PC+ colonization. The density of Hib in the upper respiratory tract lavage fluid of C57BL/6 (WT), antibody-deficient (μMT), and secretory antibody-deficient (pIgR) mice at 3 days post-Hib inoculation. The log CFU/ml of each H. influenzae strain in the lavage fluid is indicated for each mouse, and horizontal bars denote mean values. The dashed line indicates the limit of detection. Statistical differences were determined using the Mann-Whitney test (***; P < 0.001).