Recently, Heat shock proteins such as Hsp60, Hsp70, Hsp90 and gp96 have been reported to play important roles in antigen presentation, activation of lymphocytes and macrophages, and activation and maturation of dendritic cells . Here we AZD6244 cost demonstrated that plant Hsp90s function as B-cell mitogen. The kinetic patterns of plant Hsp90-induced proliferative responses of spleen cells showed that 50 mg/ml of the recombinant protein is sufficient to induce a significantly proliferative response in spleen cells from na?��ve BALB/c and C3H/HeN mice. Flow cytometry analysis of the responder cells revealed that rpHsp90s induced proliferation of B- but not of Tcells, indicating that plant Hsp90s possesses B-cell mitogenic properties. In this work, rLiHsp83 was used as a positive control because its effect on B-cells has been previously reported , showing that rpHsp90s and rLiHsp83 share similar immunostimulatory properties. Our results show for the first time how spleen cell proliferation can be stimulated by non-pathogen-derived Hsp90s. The amino acid sequences from plant Hsp90 showed high identity with its ortholog from humans and other eukaryotic organisms, supporting the idea that its function in cells is highly conserved in eukaryotes. In fact, Hsp90 purified from Brassica napus was able to bind to Hsp70/Hsp40 from rabbits and to Hop and p23 from humans . Following this line of thinking, and taking into account the high degree of sequence conservation between the plant and the parasitic Hsp90 , it is logical that eukaryotic Hsp90s share similar functions, including their immunostimulatory properties. This is similar to that observed for Hsp70, a highly conserved chaperone among eukaryotic organisms. It has been recently demonstrated that plant-derived Hsp70 ERK inhibitor shares structural and functional properties with the mammalian homolog, suggesting that Hsp70 could be an available immunological carrier . In addition, Hsp70s from T. gondii, L. infantum and Mycobacterium tuberculosis have been demonstrated to be potent mitogens for murine splenocytes . Because LPS is a well-known B-cell mitogen, a priori it cannot be discarded that the splenocyte proliferation observed by rpHsp90s was due to LPS contamination. However, rpHsp90-induced proliferative responses were not significantly inhibited by polymyxin- B, which almost completely inhibited LPS-induced proliferative responses. On the other hand, another heat shock protein, rTgHsp28 purified by the same method as rpHsp90, was unable to induce proliferation, suggesting that the low contamination with LPS in the samples were inhibited by polymyxin-B.