Abstract
CD1d-restricted invariant natural killer T cells (NKT cells) have been well characterized in humans and mice, but it is unknown whether they are present in other species. Here we describe the invariant TCR α chain and the full length CD1d transcript of pig and horse. Molecular modeling predicts that porcine (po) invariant TCR α chain/poCD1d/α-GalCer and equine (eq) invariant TCR α chain/eqCD1d/α-GalCer form complexes that are highly homologous to the human complex. Since a prerequisite for the presence of NKT cells is the expression of CD1d protein, we performed searches for CD1D genes and CD1d transcripts in multiple species. Previously, cattle and guinea pig have been suggested to lack CD1D genes. The CD1D genes of European taurine cattle (Bos taurus) are known to be pseudogenes because of disrupting mutations in the start codon and in the donor splice site of the first intron. Here we show that the same mutations are found in six other ruminants: African buffalo, sheep, bushbuck, bongo, N’Dama cattle, and roe deer. In contrast, intact CD1d transcripts were found in guinea pig, African elephant, horse, rabbit, and pig. Despite the discovery of a highly homologous NKT/CD1d system in pig and horse, our data suggest that functional CD1D and CD1d-restricted NKT cells are not universally present in mammals.
Highlights
CD1d proteins are expressed on the surface of a variety of antigen presenting cells and non-hematopoietic cells, and present cellular self-lipids and exogenous lipids with an ␣-anomerically linked sugar to T cells with a highly conserved, invariant TCR, NKT cells
First strand cDNA was synthesized with Multiscribe reverse transcriptase (Applied Biosystems) from RNA isolated with the Qiagen RNAEasy kit from freshly isolated PBMC from cattle, sheep, pig (Sus scrofa), horse (Equus caballus), guinea pig (Cavia porcellus), cat (Felis catus), rabbit (Oryctolagus cuniculus), and African elephant (Loxodonta africana)
The other two hits did not contain any sequence upstream of the ␣1 domain. From this we conclude that in the EST database there are no functional CD1D transcripts corresponding to the AJ006722 sequence, but there are transcripts of the pseudogene we describe in this paper
Summary
CD1d proteins are expressed on the surface of a variety of antigen presenting cells and non-hematopoietic cells, and present cellular self-lipids and exogenous lipids with an ␣-anomerically linked sugar to T cells with a highly conserved, invariant TCR, NKT cells. Natural exogenous ligands for NKT cells presented by CD1d have been identified, such as GSL-I from Sphingomonas species (Kinjo et al, 2005) and BbGL-II from Borrelia burgdorferi (Kinjo et al, 2006). Sphingomonas species contain antigens that are presented by CD1d to NKT cells. Sphingomonas, a genus that does not include highly pathogenic bacteria, belongs to the class of ␣proteobacteria. This class of bacteria contains peptidoglycan and LPS-negative bacteria, including pathogenic tick-borne genera: Rickettsia, Anaplasma, and Ehrlichia, all causing morbidity and mortality in livestock. None of these bacteria has been studied closely enough to determine whether they contain antigens for NKT cells. Some indigenous African breeds of cattle are more resistant to heartwater and anaplasmosis than other
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