Polysaccharide-protein conjugates have been developed to overcome the T-independent response, hyporesponsiveness to repeated vaccination, and poor immunogenicity in infants of polysaccharides. To address the impact of polysaccharide length, typhoid conjugates made with short- and long-chain fractions of Vi polysaccharide with average sizes of 9.5, 22.8, 42.7, 82.0, and 165 kDa were compared. Long-chain-conjugated Vi (165 kDa) induced a response in both wild-type and T cell-deficient mice, suggesting that it maintains a T-independent response. In marked contrast, short-chain Vi (9.5 to 42.7 kDa) conjugates induced a response in wild-type mice but not in T cell-deficient mice, suggesting that the response is dependent on T cell help. Mechanistically, this was explained in neonatal mice, in which long-chain, but not short-chain, Vi conjugate induced late apoptosis of Vi-specific B cells in spleen and early depletion of Vi-specific B cells in bone marrow, resulting in hyporesponsiveness and lack of long-term persistence of Vi-specific IgG in serum and IgG⁺ antibody-secreting cells in bone marrow. We conclude that while conjugation of long-chain Vi generates T-dependent antigens, the conjugates also retain T-independent properties, leading to detrimental effects on immune responses. The data reported here may explain some inconsistencies observed in clinical trials and help guide the design of effective conjugate vaccines.

已经开发出多糖-蛋白质结合物来克服T-非依赖性反应，对反复疫苗接种的反应低下以及多糖婴儿的免疫原性差。为了解决多糖长度的影响，比较了由Vi多糖的短链和长链级分制成的伤寒缀合物，其平均大小为9.5、22.8、42.7、82.0和165 kDa。长链缀合的Vi（165 kDa）在野生型和T细胞缺陷型小鼠中均诱导了应答，这表明它维持了T依赖性应答。与之形成鲜明对比的是，短链Vi（9.5至42.7 kDa）缀合物在野生型小鼠中引起了反应，但在T细胞缺陷型小鼠中却没有，这表明该反应取决于T细胞的帮助。从机理上讲，这在新生小鼠中得到了解释，其中长链而不是短链，⁺骨髓中分泌抗体的细胞。我们得出的结论是，虽然长链Vi的结合产生T依赖性抗原，但结合物也保留了T依赖性特性，从而导致对免疫反应的有害影响。此处报告的数据可能解释了临床试验中观察到的一些不一致之处，并有助于指导有效的结合疫苗的设计。