For example, a lower peak B. microti parasitemia was observed later in infection in coinfected as compared to B. microti young infected mice and not in old mice suggesting that innate immune response at early phase of infection against B. burgdorferi in young susceptible mice, likely induced by abundance of spirochetal lipoproteins and TLR2 signaling, contributes to decrease in erythrocytic infection cycles by this protozoan only in these mice (data not shown). The gene discussed is TLR2; the disease is infection.