High affinity (left), but not low affinity (center), virus can compete with laminin (red).

Aclose relative of Lassa fever virus (LFV) may sneak into cells by displacing the extracellular matrix molecule laminin from its normal binding partner, α-dystroglycan, according to Kunz et al. (page 301). A mutant virus with a lower binding affinity for α-dystroglycan fails to displace laminin and cannot infect the same cell types. This changes the course of the disease.

The infection with the mouse virus, lymphocytic choriomeningitis virus (LCMV), is played out primarily in the spleen. The high affinity virus infects mostly α-dystroglycan–producing dendritic cells, which normally migrate from the peripheral zone into the white pulp, where they present antigen to naive B and T cells. An infection of the dendritic cells with high affinity LCMV interferes with antigen presentation and causes immunosuppression.

To infect dendritic cells and establish a persistent infection, it appears that LCMV must wrest its cellular receptor, α-dystroglycan, away from the protein's usual partner, laminin, which is expressed in the peripheral zone of the white pulp. In vitro tests show that high affinity LCMV can displace laminin bound to α-dystroglycan on dendritic cells. But the same is not true for low-affinity virus, which cannot displace laminin and thus fails to infect dendritic cells. It is left to establish a short-term, robust infection of cells in the red pulp of the spleen.

LFV shares alot of biology with LCMV, including high affinity binding to α-dystroglycan, but causes a deadly hemorrhagic fever in humans. The authors are now looking at the expression levels of matrix proteins and α-dystroglycan on and around endothelial cells. If there are parallels with the LCMV situation in the spleen, their work may explain how LFV initiates hemorrhagic disease, and why certain strains of Lassa fever are more deadly than others. ▪