Differential pulmonic NK and NKT cell responses in Schistosoma japonicum-infected mice

Natural killer cells (NK cells) and natural killer T cells (NKT cells) play a role in anti-infection, anti-tumor, transplantation immunity, and autoimmune regulation. However, the role of NK and NKT cells during Schistosoma japonicum (S. japonicum) infection has not been widely reported, especially regarding lung infections. The aim of this study was to research the NK and NKT cell response to S. japonicum infection in the lungs of mice. Using immunofluorescent histological analysis, NK and NKT cells were found near pulmonary granulomas. Moreover, flow cytometry revealed that the percentage and number of pulmonic NK cells in S. japonicum-infected mice were significantly increased (P < 0.05). However, the percentage and cell number of NKT cells were decreased compared to those of normal mice (P < 0.05). The expression of CD69 on pulmonic NK and NKT cells was increased after infection (P < 0.05), and CD25 expression increased only on NKT cells (P < 0.05). Intracellular cytokine staining showed a higher percentage of IFN-γ⁺ and lower percentage of IL-5⁺ pulmonic NK cells (P < 0.05) compared to controls. However, the percentage of IL-17⁺, IL-10⁺, and IL-5⁺ pulmonic NKT cells significantly increased (P < 0.05). Additionally, there was a significant decrease in NKG2A/C/E (CD94) expression and an increase of NKG2D (CD314) expression on pulmonic NKT cells (P < 0.05), which might serve as a mechanism for NKT cell activation during S. japonicum infection.