CD4 and HIV-1 infection: Two distinct CD4+ T cell lineages, Th1 and Th17, facilitate clearance of S. pneumoniae carriage within the nasopharynx; CD4+ T cell depletion during HIV-1 infection has been associated with defects within the Th1 T cell compartment [25], thus compromising S. pneumoniae clearance in symptomatic HIV-1-infected individuals.