Major histocompatibility complex-independent recognition of a distinctive pollen antigen, most likely a carbohydrate, by human CD8+ alpha/beta T cells.
We have isolated CD8+ alpha/beta T cells from the blood of atopic and healthy individuals which recognize a nonpeptide antigen present in an allergenic extract from Parietaria judaica pollen. This antigen appears to be a carbohydrate because it is resistant to proteinase K and alkaline digestion, is hydrophilic, and is sensitive to trifluoromethane-sulphonic and periodic acids. In addition, on a reverse-phase high performance liquid chromatography column the antigen recognized by CD8(+) T cells separates in a fraction which contains >80% hexoses (glucose and galactose) and undetectable amounts of proteins. Presentation of this putative carbohydrate antigen (PjCHOAg) to CD8+ T cell clones is dependent on live antigen presenting cells (APCs) pulsed for >1 h at 37 degrees C, suggesting that the antigen has to be internalized and possibly processed. Indeed, fixed APCs or APCs pulsed at 15 degrees C were both unable to induce T cell response. Remarkably, PjCHOAg presentation is independent of the expression of classical major histocompatibility complex (MHC) molecules or CD1. CD8+ T cells stimulated by PjCHOAg-pulsed APCs undergo a sustained [Ca2+]i increase and downregulate their T cell antigen receptors (TCRs) in an antigen dose- and time-dependent fashion, similar to T cells stimulated by conventional ligands. Analysis of TCR Vbeta transcripts shows that six independent PjCHOAg-specific T cell clones carry the Vbeta8 segment with a conserved motif in the CDR3 region, indicating a structural requirement for recognition of this antigen. Finally, after activation, the CD8+ clones from the atopic patient express CD40L and produce high levels of interleukins 4 and 5, suggesting that the clones may have undergone a Th2-like polarization in vivo. These results reveal a new class of antigens which triggers T cells in an MHC-independent way, and these antigens appear to be carbohydrates. We suggest that this type of antigen may play a role in the immune response in vivo.
Corinti
S
S
Laboratorio di Immunologia, Istituto Superiore di Sanità, I-00161 Roma, Italy.
De Palma
R D
RD
Fontana
A
A
Gagliardi
M C
MC
Gagliardi
C
C
Pini
C
C
Sallusto
F
F
D000485:Allergens / Q000737:chemistry* / Q000302:isolation & purification; D000595:Amino Acid Sequence; D017951:Antigen Presentation; D001483:Base Sequence; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002241:Carbohydrates / Q000737:chemistry / Q000276:immunology; D002999:Clone Cells; D004247:DNA / Q000235:genetics; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000276:immunology; D008285:Major Histocompatibility Complex; D008969:Molecular Sequence Data; D011058:Pollen / Q000737:chemistry* / Q000276:immunology*; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics / Q000378:metabolism
D000485:Allergens; D002241:Carbohydrates; D016693:Receptors, Antigen, T-Cell, alpha-beta; D004247:DNA