Melatonin and Indole-3-Propionic Acid Reduce Surface FcγRIII/CD16-Related Parameters in Porcine Peripheral Blood Mononuclear Cells In Vitro

FcγRIII (CD16) is expressed by several leukocyte populations, including monocytes, macrophages, and natural killer cells, and plays an important role in IgG-mediated immune responses. Altered CD16 expression has been reported in inflammatory and autoimmune conditions, including thyroid-associated immune alterations. This preliminary in vitro study investigated whether the indole-derived compounds melatonin and indole-3-propionic acid (IPA) affect surface FcγRIII/CD16-related parameters in porcine peripheral blood mononuclear cells (PBMCs) cultured alone or with autologous thyroid follicular cells. PBMCs were left untreated or treated with melatonin or IPA, both at 50 µM, and analysed by flow cytometry at baseline and after 24 and 48 h of culture. The percentage of CD45⁺CD16⁺ cells and the CD16 mean fluorescence intensity were assessed as surface CD16-related parameters. Untreated PBMC cultures showed a time-dependent decrease in both the percentage of CD45⁺CD16⁺ cells and CD16 mean fluorescence intensity. Melatonin and IPA further enhanced this decrease compared with untreated cultures. Co-culture with thyroid follicular cells did not significantly modify CD16-related parameters under the tested conditions. These findings suggest that melatonin and IPA may modulate the surface CD16-related phenotype of porcine CD45⁺ leukocytes in vitro. The results provide preliminary evidence for the potential immunomodulatory activity of indole-derived compounds within the CD16-expressing leukocyte compartment and warrant further investigation in extended experimental models.