Abstract We examined the expression of interleukin-6 in the gastrointestinal tract,liver and esophagus in rhesus macaques infected with Streptococcus pneumoniae spontaneously.The pathogenesis of streptococcus pneumonia and features of spontaneous Streptococcus pneumoniae infection are discussed.Using common H & E staining,general histological and pathological changes were detected,and the changes of interleukin-6 expression in liver,stomach,jejunum,caecum and esophagus were analyzed by immunohistochemistry and in situ hybridization. All of the organs inspected showed inflammatory reactions. Hepatic tissue and enteradans were necrotic。The liver,jejunum and caecum showed obvious hemorrhage and hyperemia.Many inflammatory cells infiltrated the gastrointestinal tract. Compared with normal control groups,infected groups had significantly higher expression of interleukin-6 (P < 0.05). The total areas of positive cells in the infected groups were also significantly higher than those in normal monkeys (P <0. 05). Most of the positive cells were concentrated in the mucous layer,while in the liver,were mainly distributed around the blood vessels. Glandular cells,hepatocytes, endotheliocytes,uncuticular epitheliums and lymphocytes all showed positive reactions.As an inflammatory factor,interleukin-6 may play a role in Streptococcus pneumoniae infections and may participate in the clearance of Streptococcus pneumoniae.