T cell responses affected by aminopeptidase N (CD13)-mediated trimming of major histocompatibility complex class II-bound peptides.

Dendritic cells and human B cell lines were compared for ability to present synthetic peptides corresponding to residues 145–159 and 188–203 of human Ig κ-chains to peptide-specific mouse T cell hybridomas restricted by HLA-DR4Dw4. B cell lines presented both peptides, but dendritic cells could only efficiently present the latter epitope. In this paper, we show that dendritic cells degrade the 145–159 peptide, removing four residues from the amino terminus. Binding of the peptide to the class II restriction element is not required for this process. The degradation product is resistant to further cleavage, accumulates in the culture supernatant, and does not bind to HLA-DR4Dw4 or stimulate T cell reactivity. Cleavage can be blocked with bestatin, but not with other protease inhibitors tested, or by a mAb directed against aminopeptidase N (CD13). Addition of an acetyl group to the amino terminus of peptide 145–159 also blocks degradation, and allows dendritic cells to present the peptide to specific T cells with greatly increased efficiency. These results demonstrate that CD13 on dendritic cells is able to selectively and efficiently degrade exogenously provided peptide Ags, in a process that can be blocked by addition of an acetyl group to the amino terminus of the peptide. Modification of the amino terminus of peptide epitopes susceptible to degradation may prove to be useful as a general strategy for enhancing their immunogenicity.

Section: Discussionsupporting

confidence: 80%

Modification of the Amino Terminus of a Class II Epitope Confers Resistance to Degradation by CD13 on Dendritic Cells and Enhances Presentation to T Cells

Dong¹,

B²,

L³

et al. 2000

“…After incubation with or without sCD26 for 24 h, monocytes were incubated with the indicated mAbs (5 g/ml) or CTLA-4 Ig (5 g/ ml) for 15 min at 4°C before onset of culture. of the ectopeptidases on the cell surface, may trim MHC class II-bound peptides on the surface of the APC to modify T cell responsiveness (26). However, our findings clearly show that the enhancement of TT-induced T cell proliferation by sCD26 did not result from trimming of the MHC class II-bound peptide on the APC surface, in contrast to the findings related to CD13 aminopeptidase.…”

Section: Discussioncontrasting

confidence: 56%

Soluble CD26/Dipeptidyl Peptidase IV Induces T Cell Proliferation Through CD86 Up-Regulation on APCs

Ohnuma

Munakata

Ishii

et al. 2001

CD26 is a T cell costimulatory molecule with dipeptidyl peptidase IV enzyme activity in its extracellular region. We have previously reported that the addition of soluble CD26 (sCD26) resulted in enhanced proliferation of peripheral blood T lymphocytes induced by the recall Ag, tetanus toxoid (TT). However, the mechanism involved in this immune enhancement has not yet been elucidated. In this paper, we demonstrate that the enhancing effect of sCD26 on TT-induced T cell proliferation occurred in the early stages of immune response. The cells directly affected by exogenously added sCD26 are the CD14-positive monocytes in the peripheral blood. Mannose-6 phosphate interfered with the uptake of sCD26 into monocytes, suggesting that mannose-6 phosphate/insulin-like growth factor II receptor plays a role in the transportation of sCD26 into monocytes. When sCD26 was added after Ag presentation had taken place, enhancement in TT-induced T cell proliferation was not observed. In addition, enhancement of TT-mediated T cell proliferation by sCD26 does not result from trimming of the MHC-bound peptide on the surface of monocytes. Importantly, we also showed that exogenously added sCD26 up-regulated the expression of the costimulatory molecule CD86 on monocytes through its dipeptidyl peptidase IV activity, and that this increased expression of CD86 was observed at both protein and mRNA level. Therefore, our findings suggest that sCD26 enhances T cell immune response to recall Ag via its direct effect on APCs.

“…Polypeptides capable of binding to class II molecules may be very long (7,8,41), and additional trimming of the polypeptides after class II binding may be required for efficient stimulation of these T cell hybridomas (42). Although such trimming could potentially occur through the actions of proteases at the plasma membrane (43,44), internalization of the Ag appears to be necessary for additional processing (Fig. 5) to generate the particular epitopes within this region.…”

Section: Discussionmentioning

confidence: 99%

Processing and Reactivity of T Cell Epitopes Containing Two Cysteine Residues from Hen Egg-White Lysozyme (HEL74–90)

Kang

Mikszta

Deng

et al. 2000

The Ag processing and structural requirements involved in the generation of a major T cell epitope from the hen egg-white lysozyme protein (HEL74–88), containing two cysteine residues at positions 76 and 80, were investigated. Several T cell hybridomas derived from both low responder (I-Ab) and high responder (I-Ak) mice recognize this region. These hybridomas are strongly responsive to native HEL, but unresponsive to the reduced and carboxymethylated protein. Air-oxidized HEL74–88 peptide was unable to bind I-Ak molecules and failed to stimulate T cells in the absence of intracellular Ag processing. Further functional competition assays showed that alkylation of cysteine residues with bulky methyl groups interferes with the contacts for the MHC class II molecules (I-Ak) of high responder mice and the I-Ab-restricted TCR of low responder mice. Serine substitutions of the cysteine residues of HEL74–88 either enhanced or abrogated T cell stimulation by the peptides without significant alterations in the class II binding. These results suggest that the cysteine residues of peptides must be free from disulfide bonding for efficient stimulation of T cells and yet frequently used modifications of cysteine residues may not be suitable for peptide-based vaccine development.