Differential regulation of polysaccharide-specific antibody responses to isolated polysaccharides, conjugate vaccines, and intact Gram-positive versus Gram-negative extracellular bacteria

Highlights • Antibody responses to isolated polysaccharides are T cell-independent (TI). • TI responses require both Ig crosslinking and second signals from innate immunity. • IgG responses to polysaccharides on intact bacteria are T cell-dependent (TD). • TD IgG responses to conjugate vaccines and bacteria differ mechanistically. • TD IgG responses to Gram-positive versus Gram-negative bacteria show distinct features.