〔Abstract〕 To explore the role of tumour necrosis factor(TNF) in splenic infection of mice by Leishmania major. Methods To establish an infection model, promastigotes of Leishmania were injected intradermally into the right hind foot of mice. The thickness of the footpad and body weight were measured to monitor the infection. Histological changes in the spleen after infection were observed by HE staining. Changes in lymphocytes and monocytes in the spleen were detected by flow cytometry. The expression level of Arginase-1(Arg-1) and inducible nitric oxide synthase (iNOS) in the spleen was determined by indirect immunofluorescence. The effect of TNF-α on macrophage infection with Leishmania was evaluated in vitro. Results Compared to B6.WT mice, the spleens of B6.TNF-/- mice showed significant enlargement 42 days post-infection, with structural disruption. Various cells infiltrated and were dispersed throughout the entire spleen.Flow cytometry results indicated that after infection with Leishmania, there was no significant change in the proportions of T cells and B cells in the spleens of the mice, while CD11b monocytic cells significantly increased.Immunofluorescence results revealed that the M2 macrophage/monocyte marker Arg-1 was highly expressed in the spleens of B6.TNF-/- mice (P < 0.05). The expression of iNOS in the spleens of B6.WT mice was relatively strong (P < 0.05). In vitro studies found that the absence or inhibition of TNF-α significantly increased the infection of Leishmania by peritoneal macrophages (P < 0.01), while the addition of TNF-α markedly inhibited this infection (P < 0.01). Conclusion The splenic infection in B6.TNF-/- mice following subcutaneous inoculation of L. major in the hind footpad may be associated with the absence of TNF-α, which leads to M2-type differentiation of macrophages and reduced nitric oxide (NO) production.