The risk of infection by Neisseria meningitides bacteria in a normal population is one in two million. The risk of infection by this bacterium in a particular sub-population is one in two hundred. The members of this sub-population have a deficiency in which of the following immune-system components?

MCQs on the immune system, including innate and adaptive immunity, the cells involved in each of process of the immune system and their role in the immune response, and how antibodies are used to confer immunity for future potential exposures.