Interleukin-35 (IL-35) is a protein that was recently discovered and is composed of IL-12α and IL-27β chains. It is produced by the IL12A and EBI3 genes. Interest in the study of IL-35 has grown significantly in recent years, as evidenced by numerous scientific publications. Clinical research has revealed that patients who are negative for C-peptide have significantly lower serum levels of IL-35, which is accompanied by a decrease in the proportion of IL-35+ Treg cells, regulatory B cells, and CD8+ FOXP3+ cells that produce IL-35. This article highlights the potential importance of IL-35 expression in regulating the immune response and its role in chronic inflammatory Type 1 and autoimmune diabetes in the context of pancreatic inflammation, including its ability to control cytokine proportions, regulate B cells, and provide protection against autoimmune diabetes. Nonetheless, additional research is required to determine the exact mechanism of IL-35, and clinical trials must be carefully planned.