Final answer:
TH1 cells mediate cell immunity against intracellular pathogens, activating macrophages and cytotoxic T cells. C57BL/6 mice should show a strong TH1 response to L. major infection, with IFNγ-activated macrophages killing the parasite. BALB/c mice tend to exhibit a TH2 response, which is more suited for extracellular pathogens.
Step-by-step explanation:
In understanding the immune response to Leishmania major (L. major) infection in mice, it's essential to comprehend how different T helper (TH) cells influence the immune system. TH1 cells are crucial for cell-mediated immunity, primarily responding to intracellular pathogens like Mycobacterium tuberculosis, and entail the activation and enhancement of macrophages and cytotoxic T cells. Consequently, activation of macrophages by interferon-γ (IFNγ) from TH cells would enable macrophages to eliminate intracellular parasites.
C57BL/6 mice generating a strong TH1-type response when infected with L. major is consistent with the TH1 cells' tendency to target intracellular pathogens. Therefore, we would expect that L. major infection causes a strong TH1-type response in C57BL/6 mice. Conversely, BALB/c mice are known to produce a TH2-type response, which is not ideal for dealing with intracellular pathogens like L. major but rather are suited for extracellular pathogens. Thus, a TH2-type response would be expected in BALB/c mice following L. major infection.
Lastly, the idea that L. major infection does not trigger any immune response in mice is incorrect. Both TH1 and TH2 responses are parts of the adaptive immune system and are crucial for combating various types of infections. Therefore, we expect mice to exhibit an immune response when infected with L. major.