Cholestasis and age-adjusted small bowel length are the major predictors of mortality in pediatric SBS. Age-adjusted small bowel length and ICV are the major predictors of weaning from PN. These data permit better prediction of outcomes of pediatric SBS, which may help to direct future management of these challenging patients.
Studies centered on understanding how molecular structure affects biological function have historically focused on proteins. Circular dichroism (CD) is commonly used to analyze protein secondary structure, yet its application to other molecules is far less explored. In fact, little is known about how glycan conformation might affect function, likely because of a lack of tools for measuring dynamic structural changes of carbohydrates. In the present study, we developed a method based on CD to monitor conformational changes in the zwitterionic T-cell-activating glycoantigen polysaccharide A1 (PSA). We found that PSA helical structure produces a CD spectrum that is strikingly similar to proteins rich in alpha-helical content and is equally sensitive to nonpolar solvents. Like conventional T-cell-dependent proteins, PSA requires processing before major histocompatibility complex class II (MHCII) binding. CD spectra of PSA fragments of varying sizes indicated that fragments smaller than three repeating units lack helical content and are incapable of MHCII binding. Likewise, neutralization of charged groups in the repeating unit resulted in major conformational changes as measured by CD, which correlated with a lack of MHCII presentation. These data represent two significant findings: CD can be used to measure conformational changes in carbohydrates and the functional epitope from PSA is dependent on a specific conformation that is stabilized by adjacent repeating units and a zwitterionic charge motif. As a result, this work demonstrates that CD is a valuable tool for use in functional glycomics efforts that seek to align chemical and conformational structure with biological activity.
Adaptive immune responses to proteins derived from extracellular pathogens are mediated by MHCII, leading to CD4+ T cell activation. Recently, it was demonstrated that zwitterionic polysaccharide molecules (glycoantigens), such as PSA from the capsule of B. fragilis, are also presented by MHCII and induce T cell activation. However, unpublished anecdotal data has suggested that some individuals fail to respond to glycoantigens in T cell activation assays. In the present study, blood samples were drawn from volunteers to measure T cell responsiveness as measured by proliferation and cytokine production. The data indicates that glycoantigen presentation can induce the development of a TH1 response characterized by robust production of IFNγ and T cell proliferation as previously reported in the literature. Interestingly, T cells from some individuals fail to proliferate in response to glycoantigen, yet produce high concentrations of IFNγ in a T cell-dependent fashion. These data represent the first documented evidence of differential glycoantigen-mediated T cell responses in humans and lead to questions of restriction and allelic specificity during antigen presentation. A complete understanding of the presentation and recognition of glycoantigens during T cell activation could lead to advances in vaccine design using carbohydrate antigens.
This work was supported by a grant to B.A. Cobb (AI062707).
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