Binding and Activation of CR3 Receptor by Borrelia burgdorferi 575 Interaction with Borrelia burgdorferi Causes Increased Expression of the CR3 Integrin and Increased Binding Affinity to Fibronectin via CR3

We have previously demonstrated that the αMβ2 integrin (known as CR3 or Mac-1) expressed on neutrophils (PMNs) and/or on CHO Mac-1 transfected cells,in the presence of serum complement binds B. burgdorferi and promotes an increased non -opsonic adhesion, in the presence of serum complement. In this study we demonstrate that: 1) living motile B. burgdorferi and recombinant lipidated OspA and OspC, up-regulate CR3 expression on PMNs; 2) in the absence of serum, B. burgdorferi induces increased adhesion of CHO cells expressing CR3 to fibronectin, an extracellular matrix protein. Both the I-domain and the lectin-like domain of CR3 are involved in the binding recognition and activation because mAb anti I-domain and N-acetyl-glucosamine inhibit cell adhesion to fibronectin. These data indicate that B. burgdorferi whole cells, but not Osps, activate CR3 integrin; since this receptor plays a key role in priming neutrophils to important inflammatory events, the interaction of B. burgdorferi with neutrophils via the CR3 may enhance their role both in defence and in disease.