The Forgotten: Identification and Functional Characterization of MHC Class II Molecules H2-Eb2 and RT1-Db2

Abstract

In this article, we report the complete coding sequence and to our knowledge, the first functional analysis of two homologous nonclassical MHC class II genes: RT1-Db2 of rat and H2-Eb2 of mouse. They differ in important aspects compared with the classical class II β1 molecules: their mRNA expression by APCs is much lower, they show minimal polymorphism in the Ag-binding domain, and they lack N-glycosylation and the highly conserved histidine 81. Also, their cytoplasmic region is completely different and longer. To study and compare them with their classical counterparts, we transduced them in different cell lines. These studies show that they can pair with the classical α-chains (RT1-Da and H2-Ea) and are expressed at the cell surface where they can present superantigens. Interestingly, compared with the classical molecules, they have an extraordinary capacity to present the superantigen Yersinia pseudotuberculosis mitogen. Taken together, our findings suggest that the b2 genes, together with the respective α-chain genes, encode for H2-E2 or RT1-D2 molecules, which could function as Ag-presenting molecules for a particular class of Ags, as modulators of Ag presentation like nonclassical nonpolymorphic class II molecules DM and DO do, or even as players outside the immune system.

The genome of the plague-resistant great gerbil reveals species-specific duplication of an MHCII gene

“…Predictions of the affinity of the β1, β2 and β3 MHCII molecules to Y. pestis and Y. pseudotuberculosis antigens matched the reported high affinity of rodent β2 molecules for Yersiniae epitopes [42]. Rhop-DRB3 had an equally high affinity and largely identical affinity-profile as Rhop-DRB2 .…”

“…MHCII genes each contain a proximal promoter with conserved elements (S-X-Y motifs) that are crucial for the efficient expression of the gene. We aligned the proximal promoter of the β genes of the DR locus in great gerbil and the other investigated species to establish if the integrity of the promoter was conserved as well as examining similarities and potential dissimilarities causing the previously reported differences in transcription and expression of β 1 and β 2 genes in rodents [42,44]. The alignment of the promoter region reveals the conserved structure and similarities within β 1 and β 2 genes as well as characteristic differences (Fig.…”

“…Specifically, we tested against 16 ligands derived from the F1 capsule antigen of Y. pestis , and 1 ligand from the virulence-associated Low calcium V antigen (LcrV) of Y. pestis . In addition, we compared the binding affinity of these MHCII molecules against the superantigen Y. pseudotuberculosis derived mitogen precursor (YPm) [42]. The threshold for binders was set to <500nM [47].…”

What chickens might tell us about the MHC class II system

“…The human gene pairs DQA2/DQB2 and DPA2/DPB2 were long considered to be pseudogenes based on lack of expression and polymorphism, but DQA2/DQB2 is expressed in Langerhans cells [37]. The mouse Eb2 gene is expressed at low levels in cell lines [38,39 ]. There are also two DMB genes in mouse, which are reported to have different tissue distributions [54,55].…”

“…However, there are elaborations on this theme, leading to complications that frustrate broad generalisations. For instance, human DQA and DPA (and mouse Aa) genes are highly polymorphic but DRA (and mouse Ea) are virtually monomorphic [32], most human class II haplotypes have two functional DRB genes that have survived from a larger multigene family [33], humans have DP genes which are missing or pseudogenes in mice and rats [34], mole rats have DP but not DR [35], some ruminants have another isotype DY [36], and there are genes not expressed widely, well or at all, such as human DQA2/DQB2 and DPA2/DPB2, and mouse Eb2 [37,38,39 ].…”