CD4 and hypersensitivity pneumonitis: We have previously reported that 6 months of therapy with the TNF-α inhibitor infliximab led to a decreased percentage of bronchoalveolar lavage fluid (BALF) CD4+ T cells expressing the activation marker CD69 and a reduced CD4/CD8 ratio in patients classified as responders, indicating a less intensive TH1 alveolitis.5 To further explore the immunological mechanisms behind the effects of infliximab treatment, we set out to investigate its effect on natural killer (NK) cells, CD56+ T cells and B cells.