Although studies evaluating the relationship between TH2 cell cytokines, most notably IL-13, and fibrotic sarcoidosis are unclear, C-C Motif Chemokine Ligand 18 (CCL18)—a marker of M2 macrophage activation that directly stimulates collagen production in fibroblasts—was found to be significantly elevated in BAL fluid of patients with sarcoidosis-associated pulmonary fibrosis [32,33]. This evidence concerns the gene IL13 and sarcoidosis.