Sequential Proteolytic Processing of the Capsular Caf1 Antigen of Yersinia pestis for Major Histocompatibility Complex Class II-restricted Presentation to T Lymphocytes

Abstract

We studied the mechanisms of antigen presentation of CD4 T cell epitopes of the capsular Caf1 antigen of Yersinia pestis using murine bone marrow macrophages as antigen presenting cells and T cell hybridomas specific for major histocompatibility complex (MHC) class II-restricted epitopes distributed throughout the Caf1 sequence. The data revealed diversity in the pathways used and the degrees of antigen processing required depending on the structural context of epitopes within the Caf1 molecule. Two epitopes in the carboxyl-terminal globular domain were presented by newly synthesized MHC class II after low pH-dependent lysosomal processing, whereas an epitope located in a flexible amino-terminal strand was presented by mature MHC class II independent of low pH and with no detectable requirement for proteolytic processing. A fourth epitope located between the two regions of Caf1 showed intermediate behavior. The data are consistent with progressive unfolding and cleavage of rCaf1 from the amino terminus as it traverses the endosomal pathway, the availability of epitopes determining which pool of MHC class II is preferentially loaded. The Caf1 capsular protein is a component of second generation plague vaccines and an understanding of the mechanisms and pathways of MHC class II-restricted presentation of multiple epitopes from this candidate vaccine antigen should inform the choice of delivery systems and adjuvants that target vaccines successfully to appropriate intracellular locations to induce protective immune responses against as wide a T cell repertoire as possible.

Immunogenicity of aYersinia pestisVaccine Antigen Monomerized by Circular Permutation

“…We mapped the major immunodominant major histocompatibility complex (MHC) class IIrestricted epitopes of rCaf1 in two inbred strains of mice (23 We used antigen presentation to T-cell hybridomas in vitro as a sensitive technique to study the role of cpCaf1 structure in antigenicity (23,24). We measured the responses of Caf1-specific T-cell hybridomas to cpCaf1 and rCaf1 presented by bone marrow macrophages.…”

“…Macrophages were grown from femoral bone marrow cells of BALB/c (H-2 d ) and BALB.B (H-2 b ) mice in the presence of macrophage colony-stimulating factor as described previously (12) and activated by treatment overnight with 1 ng of gamma interferon (R&D Systems, Abingdon, United Kingdom)/ml before use as antigen-presenting cells in T-cell assays. The T-cell hybridomas specific for four epitopes of Caf1 (7- (23).…”

Presentation of the candidate rheumatoid arthritis autoantigen aggrecan by antigen‐specific B cells induces enhanced CD4+ T helper type 1 subset differentiation

“…We also show that aggrecan-specific B cells are more efficient at presenting aggrecan than macrophages and, as previously reported for tetanus toxoid, 22 equally as efficient APC as DC. We, 26,59 and others (reviewed in ref. 60), have previously shown that the intracellular origin of the MHC class II molecules used to form peptide-MHC complexes can profoundly influence subsequent CD4 + T cell activation.…”

Сapsular Antigen of Yersinia Pestis

“…Позднее при изучении механизмов презен-тации CD4 T-клеточных эпитопов F1 на мо-дели макрофагов из костного мозга мышей и T-клеточных гибридом было выявлены четыре эпитопа, взаимодействующих с эукариотичес-кими белками главного комплекса гистосов-местимости (MHC) класса II и использующих различные пути презентации [73]. Два из них расположены на C-конце глобулярного доме-на (134-147 и 123-136) и презентируются вновь синтезированными антигенами MHC класса II после лизосомального процессинга при низких значениях pH.…”

“…Кроме того, формирование более выраженного по силе и протективности тимусзависимого иммунного ответа происходит, вероятно, в организме тепло-кровного животного или человека в случае попа-дания в него F1, агрегированной с тимусзависи-мыми детерминантами других белков чумного микроба или при введении очищенного препа-рата F1 в организм, ранее контактировавший с возбудителем чумы. В то же время T-клеточные эпитопы, индуцирующие клеточное звено им-мунного ответа, присутствуют и в собственной структуре субъединицы капсульного антигена [73,96]. Следует отметить, что основное значение в формировании иммунитета к чуме принадле-жит именно клеточным иммунным процессам и главным образом T-системе лимфоцитов [24].…”