Murine Butyrophilin-Like 1 and Btnl6 Form Heteromeric Complexes in Small Intestinal Epithelial Cells and Promote Proliferation of Local T Lymphocytes

Abstract

To date, few molecular conduits mediating the cross-talk between intestinal epithelial cells and intraepithelial lymphocytes (IELs) have been described. We recently showed that butyrophilin-like (Btnl) 1 can attenuate the epithelial response to activated IELs, resulting in reduced production of proinflammatory mediators, such as IL-6 and CXCL1. We here report that like Btnl1, murine Btnl6 expression is primarily confined to the intestinal epithelium. Although Btnl1 can exist in a cell surface-expressed homomeric form, we found that it additionally forms heteromeric complexes with Btnl6, and that the engagement of Btnl1 is a prerequisite for surface expression of Btnl6 on intestinal epithelial cells. In an IEL-epithelial cell coculture system, enforced epithelial cell expression of Btnl1 significantly enhanced the proliferation of IELs in the absence of exogenous activation. The effect on proliferation was dependent on the presence of IL-2 or IL-15 and restricted to IELs upregulating CD25. In the γδ T-cell subset, the Btnl1–Btnl6 complex, but not Btnl1, specifically elevated the proliferation of IELs bearing the Vγ7Vδ4 receptor. Thus, our results show that murine epithelial cell-specific Btnl proteins can form intrafamily heterocomplexes and suggest that the interaction between Btnl proteins and IELs regulates the expansion of IELs in the intestinal mucosa.

Immunoglobulin gene analysis as a tool for investigating human immune responses

“…This can be abrogated, without loss of specificity, by changing amino acids at the edge of the CDR3 156. In addition to decreasing hydrophobicity through early B cell development,84, 150, 157 we have seen a decreased hydrophobicity in memory cells compared to naïve cells,82 which would be consistent with tolerance selection during an immune response.…”

“…We have shown differences in the periphery between transitional cells (IgD+IgM+CD27−), naïve cells (IgD+IgM+CD27−), IgM memory cells (IgD+IgM+CD27+), classical switched memory cells (CD27+IgD−) and CD27− switched memory cells (IgD−CD27−)82 and others have extended this to show plasmocyte differences 83. We have also shown repertoire differences as B cells progress through bone marrow development and central tolerance 84. These studies all serve to reinforce the view that repertoire studies should be conducted on sorted cells, be class and subclass‐specific and the subjects should be age matched as well as possible.…”

“…Similarly, the level of N nucleotide addition in early B cell development is consistent between heavy, kappa and lambda chains within individuals, but differs between individuals 152. Given the apparent importance of CDR3 size to an antibody response82, 149 and to central tolerance84, 150 these interindividual differences may warrant closer inspection in studies on immune disease, vaccination and infection as they may be biomarkers of response or autoimmunity.…”

“…These complications also frustrate a definitive clustering of Ig gene sequences into “clones” so all experiments should be comparative using exactly the same methods. We have used a levenstein distance, as opposed to a hamming distance, to build hierarchical clustering dendrograms in order to reduce error introduced by sequence indel errors 84. This is important where HTS sequencing platforms are prone to homopolymer tract errors as CDR‐H3 regions often have larger homopolymer tracts.…”

“…During an immune response to vaccine the whole blood repertoire shifts toward a smaller CDR‐H3, across IgG, IgA and IgM, at the peak of the plasmablast response before returning to baseline by day 28 149. During early B cell development of IgM, between preB cells to Naïve B cells, there is also a significant decrease in CDR‐H3 size 84, 150. The size of CDR3 is determined partially by IGH gene use, and partially by factors involved in gene rearrangement at the junctions—particularly the activity of Terminal deoxynucleotidyl transferase (TdT) adding random nucleotides to the junction.…”