Type II and III receptors for immunoglobulin G (IgG) control the presentation of different T cell epitopes from single IgG-complexed antigens - PubMed (original) (raw)

Type II and III receptors for immunoglobulin G (IgG) control the presentation of different T cell epitopes from single IgG-complexed antigens

S Amigorena et al. J Exp Med. 1998.

Abstract

T cell receptors on CD4(+) lymphocytes recognize antigen-derived peptides presented by major histocompatibility complex (MHC) class II molecules. A very limited set of peptides among those that may potentially bind MHC class II is actually presented to T lymphocytes. We here examine the role of two receptors mediating antigen internalization by antigen presenting cells, type IIb2 and type III receptors for IgG (FcgammaRIIb2 and FcgammaRIII, respectively), in the selection of peptides for presentation to T lymphocytes. B lymphoma cells expressing recombinant FcgammaRIIb2 or FcgammaRIII were used to assess the presentation of several epitopes from two different antigens. 4 out of the 11 epitopes tested were efficiently presented after antigen internalization through FcgammaRIIb2 and FcgammaRIII. In contrast, the 7 other epitopes were efficiently presented only when antigens were internalized through FcgammaRIII, but not through FcgammaRIIb2. The capacity to present these latter epitopes was transferred to a tail-less FcgammaRIIb2 by addition of the FcgammaRIII-associated gamma chain cytoplasmic tail. Mutation of a single leucine residue at position 35 of the gamma chain cytoplasmic tail resulted in the selective loss of presentation of these epitopes. Therefore, the nature of the receptor that mediates internalization determines the selection of epitopes presented to T lymphocytes within single protein antigens.

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Figures

Figure 1

Selective presentation of a cryptic epitope after antigen–IgG complexes internalization through FcγRIII. IIA1.6 cells expressing either FcγRIIb2 or FcγRIII α and γ chains were cultured in the presence of increasing concentrations of CI λ repressor (fluid phase uptake, open symbols) or CI λ repressor–IgG complexes (FcR-mediated endocytosis, filled symbols). T cell hybridomas specific for a dominant epitope (IA/12–26) or a cryptic epitope (IE/12–26) from the CI λ repressor were also included in the cultures. The secretion of IL-2 by the T cell hybrids was measured after an overnight incubation. (a) Internalization through both FcRs resulted in the efficient presentation of the dominant IAd-restricted epitope, whereas only FcγRIII-expressing cells presented the IEd-restricted epitope. (b) Both transfected cell lines presented the 12–26 peptide on IAd or IEd with identical efficiencies. The data presented are representative of results obtained in three independent experiments.

Figure 2

Presentation of the IEd-restricted cryptic epitope requires the cytoplasmic tail of the FcγRIII-associated γ chain. (a) IIA1.6 cells expressing either a tail-less FcγRII (FcγRII/ic−) or a chimera composed of the extracellular and transmembrane domains of FcγRII and the cytoplasmic tail of the FcγRIII-associated γ chain (FcγRII–icγ) were assayed for presentation of free (black symbols) and IgG-complexed (white symbols) CI λ repressor. The chimera presented both the dominant IAd-restricted epitope and the cryptic IEd-restricted epitope with high efficiency when the antigen was complexed to IgG (i.e., after receptor-mediated endocytosis). The tail-less FcγRII, in contrast, presented the dominant epitope inefficiently and was completely unable to present the cryptic epitope. (b) Both transfected cell lines presented the 12–26 peptide with similar efficiencies, indicating that the levels of IAd and IEd expression in both cell lines were the same. The data presented are representative of results obtained in five independent experiments for a and two experiments for b.

Figure 3

Presentation of the dominant and cryptic epitopes are blocked by cycloheximide. IIA1.6 cells expressing either FcγRII–icγ chimeras (top) or FcγRIIb2 receptors (bottom) were incubated with CI λ repressor–IgG complexes for various time periods with (+Cx) or without (−Cx) cycloheximide. The cells were then fixed with gluteraldehyde before incubation with the T cell hybridomas for 24 h. The presentation of both the dominant and the cryptic epitopes by FcγRIII, as well as presentation of the dominant epitope by FcγRIIb2, were all blocked in the presence of cycloheximide. Therefore, both the dominant and cryptic epitopes are presented by newly synthesized MHC class II molecules. (Similar results were obtained in three independent experiments).

Figure 4

Cell activation per se does not induce presentation of the IEd-restricted epitope. (a) FcγRIIb2- and FcγRII–ic-γ chimera–expressing cells were incubated for 24 h with OVA–anti-OVA immune complexes. The cells were then incubated with increasing concentrations of 12–26 CI λ repressor peptide and the T cell hybridomas specific for the dominant (IAd 12–26) or cryptic (IEd 12–26) epitopes. The secretion of IL-2 in the cell culture supernatants was measured. Activation of FcγRII– icγ chimera–expressing cells with IC did not modify the efficiency of presentation of the 12–26 peptide. Similar results were obtained in three independent experiments. (b) Cell activation through FcγRII–icγ chimeras does not induce the presentation of the cryptic epitope after antigen internalization by fluid phase uptake. FcγRII–icγ–expressing cells were incubated overnight in the presence of 30 μg/ml CI λ repressor, with or without irrelevant OVA–anti-OVA immune complexes, in order to engage FcγRII–icγ chimeric receptors. The cells were then fixed and reincubated overnight with T cell hybridomas specific for the dominant or the cryptic epitopes. Engagement of FcγRII–icγ chimeric receptors did not induce the presentation of the IEd-restricted cryptic epitope. (c) Cell activation through surface IgG does not induce the presentation of the CI λ repressor cryptic epitope after immune complexes internalization through FcγRIIb2. Cells expressing FcγRIIb2 were incubated in the continuous presence of CI λ repressor immune complexes in the absence or presence of specific goat anti–mouse IgG2a F(ab)′2 fragments, in order to induce cell activation through endogenous surface IgG2a. Cell activation through sIgG2a did not induce presentation of the cryptic epitope by FcγRII2b-expressing cells. Error bars in b and c indicate the mean variation of T cell stimulation in two distinct experiments.

Figure 5

FcγRII–icγL35 receptors have lost the ability to induce cell activation but are still efficiently internalized. (a) The secretion of IL-2 by the IIA1.6 cells was measured after engagement of the transfected FcγRII–icγ or FcγRII–icγL35 chimeras or FcγRIIb2 by OVA–anti-OVA immune complexes. As we have previously shown, FcγRII–icγ but not FcγRIIb2 induce the secretion of IL-2 after binding to immune complexes. The L35 mutation inhibits the induction of IL-2. (b) Internalization of the HRP–anti-HRP immune complexes was measured as described in Materials and Methods. The three transfected cell lines internalized immune complexes with similar kinetics and efficiencies. Data are representative of two independent experiments.

Figure 6

Selective effect of mutation of leucine 35 to alanine on the presentation of different epitopes. (a) The presentation of the dominant and cryptic epitopes of CI λ repressor were measured on IIA1.6 cells expressing either FcγRII–icγ or FcγRII–icγL35 receptors as described in Fig. 1. Mutation of leucine 35 to alanine did not significantly affect the presentation of the IAd-restricted epitope. In contrast, it completely inhibits presentation of the IEd-restricted epitope. (b) The two transfected cell lines present the 12–26 peptide with the same efficiency to the T cell hybridomas specific for both epitopes. The data presented are representative of results obtained in three independent experiments.

Figure 7

Mutation of leucine 35 inhibits presentation of the FcγRIII-restrained epitopes, but does not affect presentation of the epitopes also presented after internalization by FcγRII. IIA1.6 cells expressing FcγRIIb2, FcγRII–icγ, or FcγRII–icγL35 were incubated with increasing concentrations of CI λ repressor immune complexes or HEL immune complexes. The presentation of two epitopes of the CI λ repressor and two epitopes of HEL were measured with the corresponding T cell hybridomas. For these four epitopes, FcγRII–icγL35 receptors behave like FcγRIIb2 and not like FcγRII–icγ chimeras. The same results were obtained in three independent experiments.

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Type II and III receptors for immunoglobulin G (IgG) control the presentation of different T cell epitopes from single IgG-complexed antigens - PubMed (original) (raw)