IFN- is important in containment of the bacteria and in formation of the tubercle. Sometimes the disease progresses to an extrapulmonary form in which the bacteria disseminate to the bone, urogenital system, meninges, or skin. Humoral immunity is most effective against extracellular parasites, while cell-mediated immunity is most effective against intracellular parasites. It is vital to keep this in mind when developing vaccines. In man, sporozoites from an infected mosquito infect hepatocytes within 30 minutes, divide repeatedly and form schizonts which rupture and release merozoites .
Merozoites infect rbc, divide rapidly, lyse the infected rbc and release many more merozoites.
Some merozoites develop into the sexual stages of and gametocytes which are ingested by a mosquito during blood meal. In areas that are endemic for malaria, individuals may have very high titer of anti-malarial Ab, but still become reinfected. 3.Vaccine Attempts Irradiated sporozoites provide very good protective immunity against challenge with virulent parasites. Initial attempts used the repeat regions in a vaccine since these are the major B-cell epitope against which Ab are made. They do NOT contain a T cell epitope, so low levels of Ab were made.