Human CD3γ, but not CD3δ, haploinsufficiency differentially impairs γδ versus αβ surface TCR expression

Miguel Muñoz-Ruiz,Verónica Pérez-Flores,Alberto C Guardo,Ozden Sanal,Chaim M Roifman,Eduardo Martínez-Naves,Eduardo López-Granados,María J Recio,Marina S Mazariegos,Luis M Allende,Beatriz Garcillán,Sara S Kilic,Edgar Fernández-Malavé,José R Regueiro,Hidetoshi Takada

doi:10.1186/1471-2172-14-3

Abstract

BackgroundThe T cell antigen receptors (TCR) of αβ and γδ T lymphocytes are believed to assemble in a similar fashion in humans. Firstly, αβ or γδ TCR chains incorporate a CD3δε dimer, then a CD3γε dimer and finally a ζζ homodimer, resulting in TCR complexes with the same CD3 dimer stoichiometry. Partial reduction in the expression of the highly homologous CD3γ and CD3δ proteins would thus be expected to have a similar impact in the assembly and surface expression of both TCR isotypes. To test this hypothesis, we compared the surface TCR expression of primary αβ and γδ T cells from healthy donors carrying a single null or leaky mutation in CD3G (γ+/−) or CD3D (δ+/−, δ+/leaky) with that of normal controls.ResultsAlthough the partial reduction in the intracellular availability of CD3γ or CD3δ proteins was comparable as a consequence of the mutations, surface TCR expression measured with anti-CD3ε antibodies was significantly more decreased in γδ than in αβ T lymphocytes in CD3γ+/− individuals, whereas CD3δ+/− and CD3δ+/leaky donors showed a similar decrease of surface TCR in both T cell lineages. Therefore, surface γδ TCR expression was more dependent on available CD3γ than surface αβ TCR expression.ConclusionsThe results support the existence of differential structural constraints in the two human TCR isotypes regarding the incorporation of CD3γε and CD3δε dimers, as revealed by their discordant surface expression behaviour when confronted with reduced amounts of CD3γ, but not of the homologous CD3δ chain. A modified version of the prevailing TCR assembly model is proposed to accommodate these new data.

Highlights

The T cell antigen receptors (TCR) of αβ and γδ T lymphocytes are believed to assemble in a similar fashion in humans
Total T cell numbers were consistently lower than controls (Figure 1A) which correlated with a partial impairment of lymphocyte function (Table 1)
We have previously observed in γ−/− individuals that CD3 expression levels are overestimated when T cells are defined using antibodies against TCR-associated epitopes [7], such as BMA031 or Immu510

Summary

Introduction

The T cell antigen receptors (TCR) of αβ and γδ T lymphocytes are believed to assemble in a similar fashion in humans. Partial reduction in the expression of the highly homologous CD3γ and CD3δ proteins would be expected to have a similar impact in the assembly and surface expression of both TCR isotypes To test this hypothesis, we compared the surface TCR expression of primary αβ and γδ T cells from healthy donors carrying a single null or leaky mutation in CD3G (γ+/−) or CD3D (δ+/−, δ+/leaky) with that of normal controls. If both the αβ and the γδ TCR isotypes use identical amounts of CD3γε and CD3δε, decreased availability of CD3γ or CD3δ proteins, as observed in heterozygous carriers of mutations in CD3 genes [3], would be expected to have a similar impact on the assembly and surface expression of both αβ and γδ TCR isotypes To test this hypothesis, we compared TCR surface levels of primary αβ and γδ T cells from healthy haploinsufficient donors carrying null or leaky mutations in CD3G (γ+/−) or CD3D (δ+/−, δ+/leaky). The results did not support the hypothesis of a similar impact on both TCR isotypes, but rather suggested a differential CD3γε and CD3δε usage scheme for each TCR isotype

Methods

Results

Discussion

Conclusion