Pure polysaccharide vaccines are a type of inactivated subunit vaccine composed of sugar molecules. They primarily trigger which type of immune response?

• A. They trigger a T cell dependent immune response
• B. They trigger a T cell independent immune response
• C. They require activation of B cells only with T cell help
• D. They always require boosters every year

Answer: (B)

Polysaccharide antigens activate B cells directly without helper T cells. The repeated sugar units cross-link B cell receptors and stimulate a T cell independent response, producing mainly IgM with little class switching, affinity maturation, or durable memory. That’s why pure polysaccharide vaccines often don’t generate strong, long-lasting immunity, especially in young children, and why strategies like conjugating the polysaccharide to a protein are used to recruit T cell help and produce a more robust, memory-rich response. Not all T cell dependent needs are met by these vaccines, and booster requirements are not inherently yearly; the key feature is the lack of T cell help leading to a TI response.