Review Question - QID 106881

Adults with sickle cell disease are functionally asplenic, and therefore has increased susceptibility to encapsulated bacteria. Patients with C3 complement deficiency are also more susceptible to infection with these organisms.

Encapsulated bacteria, such as H. influenzae, N. meningiditis, S. pneumonia, S. typhi, and group B strep, possess a polysaccharide capsule that allows them to evade death from cell-mediated immunity. Since infection prevention is dependent on antibody-mediated attack, conditions that affect this pathway lead to an increased susceptibility to encapsulated bacteria. In functionally asplenia, patients are unable to clear bacteria that have been tagged with antibodies. C3 complement deficiency and B-cell deficiency likewise hinder antibody-mediated immunity, and therefore also increase the risk of infection with these organisms.

Illustration A demonstrates the subunits of the conjugated meningococcal vaccine. Illustration B depicts the typical, slimy growth of encapsulated bacteria on a petri dish, in contrast to the non-capsulated bacteria in Illustration C.

Incorrect Answers:
Answer 1: Patients with C5-9 complement deficiency have an increased susceptibility to Neisseria species.
Answer 2: Patients with T-cell deficiency have increase susceptibility to intracellular organisms.
Answers 4-5: Neither hemophilia A nor hemophilia B confers and increased sensitivity to encapsulated bacteria.