Characterization of T-cell responses to the house dust mite allergen Der p II in mice. Evidence for major and cryptic epitopes (1)
Several factors have been identified that can determine the immunogenicity of a peptide epitope. These include antigen-processing by antigen-presenting cells (APC), the association of peptide with the class II MHC molecule, V gene repertoire of the responding T cells, and competition for binding of a foreign peptide to the class II molecule from other peptides.
B10 and BALB MHC congenic mice were accordingly immunized with 100 ug of Der p II in CFA at the base of tail and depending on the experiment the draining lymph nodes were removed after 8-10 days and examined for the production of IL-3/GM-CSF in response to antigen. In both congenic series H-2b mice were high responders, H-2d low responders and H-2k were intermediate.
The high responder B10 group recognized three epitopes, the major response was to peptides 78-104 and 87-112 (which means the minimal epitope is somewhere between 87 and 104), 11-35 and 105-129. The B10.A(5R) mice recognized similar determinants as the B10 mice, i.e. 87-104 and 105-129. B10.BR mice recognized two epitopes with 36-50 eliciting strongest responses (an overlap between peptides 22-50 and 36-60), while the other was 87-104. Sensitized T cells from the low-responder H-2d mice (B10.D2) mice recognized weakly, a single peptide 36-60, while B10.A(4R) mice did not produce any significant reactions.
T cells from H-2b and H-2k mice may be responding to two distinct epitopes within the 87-104 (and 36-50 for H-2k) region and hence finer mapping is required for these areas in both haplotypes.
BO0 and BI0.BR mice were immunized with peptides 78-104 or 105-129 and 36-60 or 78-104 respectively (which represent peptides spanning immunodominant regions), the lymph node cells taken from these mice could respond efficiently to the peptide, but showed a very poor ability to be stimulated with the native antigen.
Response to the protein could however be recalled if spleen-adherent cells were added to the culture. B10 response to p78-104 and p 105-129 and for B10.BR to p22-50 and p78-104 were obtained. The addition of spleen adherent cells also permitted cells from mice immunized with p105-129 to respond to both the peptide and protein in vitro.
Peptides 1-20, and 22-50, not previously thought to contain epitopes, could stimulate lymph node responses that could be recalled by the immunizing peptide and the whole protein. Peptides 51-77 and 61-86 do not appear to contain T-cell epitypic sequences.
Both the B10 and BALB congenic mice showed that H-2b were high responders and H-2d low. This was confirmed for IL-3/ GM-CSF, IFN-y and IL-2. In comparison H-2k mice produce equivalent amounts of IFN-y as H-2b mice, but an intermediate IL-3/GM-CSF response and a very variable IL-2 response. The inclusion of spleen adherent cells from mice, however, permits peptide-primed lymph node cells to respond to protein. Spleen dendritic cells are responsible for the presentation of protein and that the lymph node-adherent cells can only present peptide and not protein.