Biology subjects

Morch, A. M.

Publications and source records attributed to Morch, A. M..

3 recordsLinked to original sources

bioRxiv2024

RIFINs displayed on malaria-infected erythrocytes bind both KIR2DL1 and KIR2DS1

To discriminate between our own cells and foreign cells such as a pathogen, natural killer cells are armed with inhibitory and activating immune receptors. In some cases, such as the KIRs, these are found in pairs, with inhibitory and activating receptors containing nearly identical extracellular domains that are coupled to different intracellular signalling domains1. The balance in signalling mediated by these receptors determines whether an NK cell is activated to destroy a target cell. Previous studies have shown that RIFINs, displayed on surfaces of Plasmodium falciparum-infected erythrocytes, can bind to inhibitory immune receptors and dampen NK cell activation2,3, reducing parasite killing. Here, we identify a clade of RIFINs that bind to inhibitory immune receptor KIR2DL1 approximately ten-times more strongly than KIR2DL1 binds its host ligand, MHC class I. We show that this interaction mediates inhibitory signalling and reduces activation of KIR2DL1-expressing NK cells. We reveal the structural basis for KIR2DL1 binding and show that the RIFIN binding surface of KIR2DL1 is conserved in the activating immune receptor KIR2DS1. We find that KIR2DL1-binding RIFINs can also bind to KIR2DS1 and that these RIFINs cause activation of KIR2DS1-expressing NK cells. This highlights the evolutionary battle between pathogen and host, suggesting that activating KIRs may have evolved to allow detection of red blood cells infected with Plasmodium falciparum, helping the host to clear the parasite.

microbiology↗

bioRxiv2023

Using CombiCells, a platform enabling titration and combinatorial display of cell surface ligands, to investigate the sensitivity and costimulatory requirements of TCRs and CARs

Understanding how cellular decisions by receptor/ligand interactions at cell/cell interface has been challenging because it is difficult to independently vary the surface density of multiple ligands. Here, we exploit the SpyCatcher/SpyTag split-protein system for rapid combinatorial display of native ligands on cells (Combicells). We use this platform to assess T cell antigen sensitivity and the impact of T cell co-stimulation/co-inhibition receptors. The TCR displayed much greater sensitivity to pMHC than CARs and BiTES did to CD19. While TCR sensitivity was greatly enhanced by CD2 ligand, CAR sensitivity to CD19 was primarily but more modestly enhanced by LFA-1 ligand. Lastly, we show that the PD-1/ligand engagement inhibited T cell activation triggered solely by TCR/pMHC interactions, as well as the amplified activation induced by CD2 and CD28 co-stimulation. The ability to easily produce cells with different concentrations and combinations of ligands should accelerate the study of receptor/ligand interactions at cell/cell interfaces. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=177 SRC="FIGDIR/small/545075v2_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@d1ec95org.highwire.dtl.DTLVardef@33c0forg.highwire.dtl.DTLVardef@5bfed7org.highwire.dtl.DTLVardef@1b80ee2_HPS_FORMAT_FIGEXP M_FIG C_FIG One sentence summaryUsing CombiCells, a platform for the combinatorial display of cell surface ligands, to compare T cell antigen sensitivity mediated by TCRs, CARs, and BiTEs and its dependence on co-stimulation/co-inhibition receptor ligands

immunology↗

bioRxiv2022

The kinase occupancy of T-cell coreceptors reconsidered

The sensitivity of the {beta} T-cell receptor (TCR) is enhanced by the coreceptors CD4 and CD8{beta}, which are expressed primarily by cells of the helper and cytotoxic T-cell lineages, respectively. The coreceptors bind to major histocompatibility complex (MHC) molecules and associate intracellularly with the Src-family kinase Lck, which catalyzes TCR phosphorylation during receptor triggering. Although coreceptor-kinase occupancy was initially believed to be high, a recent study suggested that most coreceptors exist in an Lck-free state, and that this low occupancy helps to effect TCR antigen discrimination. Here, using the same method, we found instead that the CD4-Lck interaction was stoichiometric (~100%) and that the CD8{beta}-Lck interaction was also substantial (~60%). We confirmed our findings in live cells using fluorescence cross-correlation spectroscopy (FCCS) to measure coreceptor-Lck co-diffusion in situ. After introducing structurally guided mutations into the intracellular domain of CD4, we used FCCS to show that stoichiometric Lck coupling required an amphipathic -helix present in CD4 but not CD8. In double-positive cells expressing equal numbers of both coreceptors, but limiting amounts of kinase, CD4 out-competed CD8{beta} for Lck. In T cells, TCR signaling induced CD4-Lck oligomerization but did not affect the high levels of CD4-Lck occupancy. These findings help settle the question of kinase occupancy and suggest that the binding advantages that CD4 has over CD8 could be important when Lck levels are limiting. Significance statementCD4 and CD8{beta} are archetypal coreceptor proteins that potently enhance T-cell antigen sensitivity but how they function is still debated. A fundamental question that remains incompletely resolved is: what fractions of the coreceptors bind the signal-initiating kinase, Lck? Using in vitro assays and non-invasive fluorescence fluctuation spectroscopy in live cells, we show that most coreceptors are occupied by Lck at the surface of live cells. The structural basis for important differences in the kinase occupancy of CD4 and CD8{beta} is also identified. These results provide important context for refining current models of both TCR antigen recognition and cell fate decisions made during thymopoiesis.

immunology↗