Exogenous Heat Shock Proteins HSPA1A and HSPB1 Interact with TLR2, TLR4, TLR5, and TLR7 on Differentiated U937 Monocytic Cells

Biological cells are sensitive to both pathological and non-pathological stress, which can activate the innate immune response. This activation often involves the release of heat shock proteins (HSPs), such as HSPA1A and HSPB1. However, the implications and relationships between HSP release and immune system activation remain unclear. While evidence suggests that HSPs play a role in immune system activation and regulation, their immune regulatory characteristics are still debated. Antigen-presenting cells (APCs) are a vital component of the immune system, utilizing recognition receptors such as toll-like receptors (TLRs). There is evidence that HSPs interact with CD91 and CD40 to activate the immune system. However, the potential promiscuity of HSP interactions with recognition receptors raises questions about their biological function. To investigate additional receptors involved in HSP-induced cytokine secretion, either HSPA1A or HSPB1 was exposed to differentiated U937 cells. U937 differentiated cells, along with HSPA1A or HSPB1, were preincubated with TLR2, TLR4, TLR5, and TLR7 blocking peptides. Subsequently, HSP or HSP-blocking peptide mixtures were applied to the cells, followed by the measurement of secreted IL-1β, TNF-α, and IL-10 via ELISA. The results showed a partial decrease in the HSPA1A and HSPB1-induced cytokine secretion with the blocking peptides. Indicating, some level of HSPA1A and HSPB1 interaction with the TLR2, TLR4, TLR5, and TLR7 in differentiated monocytic U937 cells.