Biology subjects

Grönloh, M. L. B.

Publications and source records attributed to Grönloh, M. L. B..

3 recordsLinked to original sources

bioRxiv2026

C1q-mediated steric hindrance limits FcγR contribution to antibody-driven phagocytosis by human neutrophils

Phagocytosis and killing of bacteria by neutrophils is a key driver of human immunity against invading infections. IgG antibodies targeting the bacterial surface can potently enhance phagocytic uptake by engaging Fc gamma receptors (Fc{gamma}Rs) on the neutrophil membrane. In addition, IgG-mediated complement activation triggers surface deposition of complement opsonins that engage complement receptors (CRs) to further enhance target cell clearance. In this paper, we reveal that complement deposition prevents engagement of Fc{gamma}Rs to the Fc-domain of surface-bound IgG molecules. When complement is present, we observe that blockade of Fc{gamma}Rs does not influence phagocytosis of both Gram-positive and -negative bacteria (using Staphylococcus aureus and Klebsiella pneumoniae as model organisms). Complement-mediated hindrance of Fc{gamma}R engagement was observed in different model conditions, for example using either pre-existing polyclonal antibodies in human serum or recombinant monoclonal antibodies (mAbs) targeting different bacterial antigens. Using Fc engineering, we found that inhibition of Fc{gamma}R binding is dependent on the ability of IgGs to form IgG hexamers. Mechanistically, we show that complement proteins, in particular C1q, directly prevents the interaction between IgG-Fc and Fc{gamma}R by steric hindrance. Together, these insights help us define the respective roles of Fc{gamma}R and CR in neutrophil phagocytosis, while also providing important fundamental insights for therapeutic antibody development.

immunology↗

bioRxiv2022

Endothelial transmigration hotspots limit vascular leakage through heterogeneous expression of ICAM1

Upon inflammation, leukocytes leave the circulation by crossing the endothelial monolayer at specific transmigration hotspot regions. Although these regions support leukocyte transmigration, their functionality is not clear. We found that endothelial hotspots function to limit vascular leakage during transmigration events. Using the photo-convertible probe mEos4b, we traced back and identified original endothelial transmigration hotspots. Using this method, we show that the heterogeneous distribution of ICAM-1 determines the location of the transmigration hotspot. Interestingly, loss of ICAM-1 heterogeneity either by CRISPR/Cas9-induced knockout of ICAM-1 or equalizing the distribution of ICAM-1 in all endothelial cells results in loss of TEM hotspots but not necessarily in reduced TEM events. Functionally, loss of endothelial hotspots results in increased vascular leakage during TEM. Mechanistically, we demonstrate that the 3 extracellular Ig-like domains of ICAM-1 are crucial for hotspot recognition. However, the intracellular tail of ICAM-1 and the 4th Ig-like dimerization domain are not involved, indicating that intracellular signalling or ICAM-1 dimerization is not required for hotspot recognition. Together, we discovered that hotspots function to limit vascular leakage during inflammation-induced extravasation.

immunology↗

bioRxiv2020

Myosin-X is required for integrin activation at filopodia tips

Filopodia assemble unique integrin-adhesion complexes to sense the extracellular matrix. However, the mechanisms of integrin localization and regulation in filopodia are poorly defined. Here, we observed that active integrins accumulate at the tip of myosin-X(MYO10)-positive filopodia while inactive integrins are uniformly distributed. RNAi depletion of 10 integrin activity modulators identified talin as the principal integrin activator in filopodia. Deletion of the MYO10-FERM domain, or mutation of the {beta}1-integrin-binding residues within, revealed MYO10 as facilitating integrin activation but not transport in filopodia. However, MYO10-FERM alone could not activate integrins, potentially due to dual binding to both a- and {beta}-integrin tails. As swapping MYO10-FERM with talin-FERM enabled integrin activation in filopodia, our data indicate that an integrin-binding FERM domain coupled to a myosin motor is a core requirement for integrin activation in filopodia. Therefore, we propose a two-step integrin activation model in filopodia: receptor tethering by MYO10 followed by talin-mediated integrin activation.

cell biology↗