<prompt> A 24-year-old woman presents with a 3-day history of fever and cough with rust-colored sputum. He had splenectomy 1 year ago. CXR film indicates consolidation of right lower lobe. Blood cultures are positive for alpha hemolytic gram-positive diplococci. Immunity to the causative organism is based onAlternative complement pathway activationAntibody to fimbriaeIgA antibodies to C carbohydrateIgG antibodies to a surface acidic polysaccharide  <response>: This is a history of pneumonia due to S. pneumoniae. The most impoant virulence factor of this organism is capsule. Therefore IgG antibodies to the capsular antigen are protective. Other virulence factors produced by pneumococcus include pneumolysin and amidase also known as suicidal enzyme. 