Idiopathic pulmonary fibrosis (IPF) is an interstitial lung disease associated with chronic inflammation and tissue remodelling leading to fibrosis, reduced pulmonary function, respiratory failure and death. Bleomycin (Blm)-induced lung fibrosis in mice replicates several clinical features of human IPF, including prominent lymphoid aggregates of predominantly B cells that accumulate in the lung adjacent to areas of active fibrosis. We have previously shown a requirement for B cells in the development of Blm-induced lung fibrosis in mice. To determine the therapeutic potential of inhibiting B cell function in pulmonary fibrosis, we examined the effects of anti-CD20 B-cell ablation therapy to selectively remove mature B cells from the immune system and inhibit Blm-induced lung fibrosis. Anti-CD20-B cell ablation did not reduce fibrosis in this model, however immune phenotyping of peripheral blood and lung resident cells revealed that anti-CD20 treated mice retained a high frequency of CD19 + CD138 + plasma cells (PCs). Interestingly, high levels of CD138 + cells were also identified in the lung tissue of patients with IPF, consistent with the mouse model. Treatment of mice with bortezomib, which depletes PCs, reduced the level of Blm-induced lung fibrosis, implicating PCs as important effector cells in the development and progression of pulmonary fibrosis.