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Our laboratory develops protocols to prevent or reverse ongoing anti-hFIX IgG inhibitors in haemophilia B mice with a F9 gene deletion on BALB/c and C3H/HeJ backgrounds. C3H/HeJ F9(-/Y) mice develop high titre anti-hFIX IgG1 inhibitors and anaphylaxis, whereas most BALB/c F9(-/Y) mice have mild anti-hFIX IgG1 inhibitors and no anaphylaxis. Our aim was to determine if hFIX-specific B- and T-cell responses in BALB/c and C3H/HeJ F9(-/Y) mice trigger the difference in anti-hFIX immune responses. BALB/c and C3H/HeJ F9(-/Y) mice were challenged weekly with recombinant hFIX protein. Humoral immune responses were determined by IgG1 and IgG2a anti-hFIX ELISA, Bethesda assay for inhibitors and B-cell ELISpot on bone marrow and spleen cells. T-cell studies measured the TH 1 (IFN-γ) and TH 2 (IL-4) cytokine responses in splenocytes at the mRNA and protein level in response to hFIX protein. Antibody responses were also measured in C3H/HeJ/OuJ F9(-/Y) mice with restored toll-like receptor 4 (TLR4) function. BALB/c F9(-/Y) mice have a TH 2 skewed response and a reduction in anti-hFIX secreting plasma cells in the bone marrow. Independent antigen challenge revealed both strains generated equivalent IgG1 antibody titres to an intravenously delivered antigen. C3H/HeJ F9(-/Y) mice have a mixed TH 1 and TH 2 response (mainly TH 2). Importantly, TLR4 signalling has a modulatory role in the C3H background on the levels of anti-hFIX IgG1 and incidence of anaphylaxis. The background strain strongly impacts the immune response to hFIX, which can be significantly impacted by mutations in innate immune sensors.
Sack et al. (Sun,) studied this question.