Biology subjects

St. Laurent, C. D.

Publications and source records attributed to St. Laurent, C. D..

5 recordsLinked to original sources

bioRxiv2026

Siglec-G on B cells restrains the germinal center response by controlling T cell help during positive selection

The germinal center (GC) reaction requires tight regulation of B cell and T follicular helper (Tfh) cell interactions to ensure B cell expansion and antibody affinity maturation, while preventing oncogenesis. However, regulatory mechanisms fine-tuning B-T cell interactions within the GC to prevent aberrant activation and proliferation remain incompletely understood. Here, we identify Siglec-G, the mouse ortholog of human Siglec-10, as an immune checkpoint that restrains the GC by dampening B-T cell interactions. Selective and temporal ablation of Siglec-G on B cells after immunization triggers GC hyperplasia and enhanced plasma cell and antibody output. While Siglec-G is dispensable in B cell receptor (BCR)-mediated processes, it acts as an intrinsic inhibitory receptor of B-T cell interactions in the GC, ultimately limiting Myc and mTORC activation within positively selected GC B cells. Trans interactions of Siglec-G and its glycan ligands on Tfh likely contribute in fine-tuning the strength of bidirectional signaling following contact between GC B cells and Tfh cells. This interaction is further reinforced by glycan remodeling that occurs in the GC, resulting in concurrent decreased in glycan ligands on GC B cells and increased in glycan ligands on Tfh. This augmented binding of Siglec-G/10 on Tfh is mainly due to the upregulation of 2-6 linked sialic acid ligands. Moreover, APEX2-based proximity labeling revealed several candidate Siglec-G/10 binding partners on T cells, including BTLA, CD6, and Slamf6, which are known negative regulators of Tfh cell activation. Taken together, our findings identified that Siglec-G acts as a GC checkpoint receptor, restricting B cell proliferation by tuning T cell help following B-T cell interactions.

immunology↗

bioRxiv2025

An ultrasensitive and modular platform to detect Siglec ligands and control immune cell function

Siglecs are immunomodulatory receptors that regulate immune cell function. A fundamental challenge in studying Siglec-ligand interactions is the low affinity of Siglecs for their ligands. Inspired by how nature uses multivalency, we developed Siglec-liposomes as a highly multivalent and versatile platform for detecting Siglec glycan ligands in which recombinant Siglecs were conjugated to liposomes using the SpyCatcher-SpyTag system. Siglec-liposomes offer tunable multivalency and a modular assembly, enabling presentation of different Siglecs on the same liposome. Using Siglec-liposomes, we profiled Siglec ligands on human leukocytes, revealing new insights into Siglec ligands. Moreover, Siglec-liposomes are in vivo compatible, where we demonstrated that Siglec-7-liposomes bind to the brain vasculature in a mucin-dependent manner. Given the abundance of Siglec ligands on T cells, we investigated whether Siglec-liposomes modulate T cell function and find that Siglec-7-liposomes increase T cell proliferation in a ST3Gal1-dependent and CD43-independent manner. Taken together, Siglec-liposomes are a versatile and sensitive tool for detecting Siglec ligands and immunomodulation.

biochemistry↗

bioRxiv2023

Alzheimer's disease associated isoforms of human CD33 distinctively modulate microglial cell responses in 5XFAD mice

Microglia play diverse pathophysiological roles in Alzheimers disease (AD), with genetic susceptibility factors skewing microglial cell function to influence AD risk. CD33 is an immunomodulatory receptor associated with AD susceptibility through a single nucleotide polymorphism that modulates mRNA splicing, skewing protein expression from a long protein isoform (CD33M) to a short isoform (CD33m). Understanding how human CD33 isoforms differentially impact microglial cell function in vivo has been challenging due to functional divergence of CD33 between mice and humans. We address this challenge by studying transgenic mice expressing either of the human CD33 isoforms crossed with the 5XFAD mouse model of amyloidosis and find that human CD33 isoforms have opposing effects on the response of microglia to amyloid-{beta} (A{beta}) deposition. Mice expressing CD33M have increased A{beta} levels, mo7re diffuse plaques, fewer disease-associated microglia, and more dystrophic neurites compared to control 5XFAD mice. Conversely, CD33m promotes plaque compaction and microglia-plaque contacts, and minimizes neuritic plaque pathology, highlighting an AD protective role for this isoform. Protective phenotypes driven by CD33m are detected at an earlier timepoint compared to the more aggressive pathology in CD33M mice that appears at a later timepoint, suggesting that CD33m has a more prominent impact on microglia cell function at earlier stages of disease progression. In addition to divergent roles in modulating phagocytosis, scRNAseq and proteomics analyses demonstrate that CD33m+ microglia upregulate nestin, an intermediate filament involved in cell migration, at plaque contact sites. Overall, our work provides new functional insights into how CD33, as a top genetic susceptibility factor for AD, modulates microglial cell function.

neuroscience↗

bioRxiv2021

Carbohydrate sulfation as a mechanism for fine-tuning Siglec ligands

The immunomodulatory family of Siglecs recognize sialic acid-containing glycans as self, which is exploited in cancer for immune-evasion. The biochemical nature of Siglec ligands remains incompletely understood with emerging evidence suggesting the importance of carbohydrate sulfation. Here, we investigate how specific sulfate modifications affect Siglec ligands by overexpressing eight carbohydrate sulfotransferases (CHSTs) in five cell lines. Overexpression of three CHSTs (CHST1, CHST2, or CHST4) significantly enhances the binding of numerous Siglecs. Unexpectedly, two other CHSTs (Gal3ST2 and Gal3ST3) diminish Siglec binding, suggesting a new mode to modulate Siglec ligands via sulfation. Results are cell type dependent, indicating that the context in which sulfated glycans are presented is important. Moreover, pharmacological blockade of N- and O-glycan maturation reveals a cell type-specific pattern of importance for either class of glycan. Production of a highly homogenous CD33 (Siglec-3) fragment enabled a mass spectrometry-based binding assay to determine 10-fold and 3-fold enhanced affinity for Neu5Ac2-3(6-O-sulfo)Gal{beta}1-4GlcNAc and Neu5Ac2-3Gal{beta}1-4(6-O- sulfo)GlcNAc, respectively, over Neu5Ac2-3Gal{beta}1-4GlcNAc. CD33 showed significant additivity in affinity (36-fold) for the disulfated ligand, Neu5Ac2-3(6-O-sulfo)Gal{beta}1-4(6-O-sulfo)GlcNAc. Moreover, overexpression of both CHST1 and CHST2 in cells greatly enhanced the binding of several Siglecs, including CD33. Finally, we reveal that CHST1 is upregulated in numerous cancers, correlating with poorer survival rates and sodium chlorate sensitivity for the binding of Siglecs to cancer cell lines. These results provide new insights into carbohydrate sulfation as a modification that is a general mechanism for tuning Siglec ligands on cells, including in cancer.

immunology↗

bioRxiv2021

Increasing phagocytosis of microglia through targeting CD33 with liposomes displaying glycan ligands

CD33 is an immunomodulatory receptor expressed on microglia and genetically linked to Alzheimers disease (AD) susceptibility. While antibodies targeting CD33 have entered clinical trials to treat neurodegeneration, it is unknown whether the glycan-binding properties of CD33 can be exploited to modulate microglia. Here, we use liposomes that multivalently display glycan ligands of CD33 (CD33L liposomes) to engage CD33. We find that CD33L liposomes increase phagocytosis of cultured monocytic cells and microglia in a CD33-dependent manner. Enhanced phagocytosis strongly correlates with loss of CD33 from the cell surface and internalization of liposomes. Increased phagocytosis by treatment with CD33L liposomes is dependent on a key intracellular signaling motif on CD33 as well as the glycan-binding ability of CD33. These effects are specific to trans engagement of CD33 by CD33L liposomes, as cis engagement through insertion of lipid-linked CD33L into cells produces the opposite effect on phagocytosis. Moreover, intracerebroventricular injection of CD33L liposomes in mice enhances phagocytosis of microglia in a CD33-dependent manner. These results demonstrate that multivalent engagement of CD33 with glycan ligands can modulate microglial cell function.

immunology↗