Oligochitosan, which has greater than 3 but less than 10 saccharide (N-acetylglucosamine or glucosamine) residues, is obtained by either chemical or enzymatic hydrolysis of chitosan. In this work, we demonstrated that oligochitosan had an in vitro stimulatory effect on the release of tumor necrosis factor-alpha and interleukin-1 beta in macrophages. Moreover, we observed that oligochitosan could be uptaken by macrophages through confocal laser microscopy. Scatchard analysis of internalization of 2-aminoacridone-oligochitosan in macrophages indicated its internalization was mediated by a specific receptor on macrophage membrane with a K-d of 2.1 x 10(-5) M. Competition studies showed that mannose could inhibit oligochitosan internalization, while lipopolysaccharide and beta-glucan could not do it. Inhibition of mannose-BSA, fucose-BSA, and N-acetylglucosamine-BSA on oligochitosan internalization further suggests that oligochitosan internalization is mediated by a macrophage lectin receptor like with mannose specificity. (C) 2004 Elsevier Inc. All rights reserved.