Truncated EphA2 likely potentiates cell adhesion via integrins as well as infiltration and/or lodgment of a monocyte/macrophage cell line in the red pulp and marginal zone of the mouse spleen, where ephrin-A1 is prominently expressed in the vasculature.

We previously established a J774.1 monocyte/macrophage subline expressing a truncated EphA2 construct lacking the kinase domain. We demonstrated that following ephrin-A1 stimulation, endogenous EphA2 promotes cell adhesion through interaction with integrins and integrin ligands such as ICAM1 and that truncated EphA2 potentiates the adhesion and becomes associated with the integrin/integrin ligand complex. Based on these findings, we hypothesized that the EphA/ephrin-A system, particularly EphA2/ephrin-A1, regulates transendothelial migration/tissue infiltration of monocytes/macrophages, because ephrin-A1 is widely recognized to be upregulated in inflammatory vasculatures. To evaluate whether this hypothesis is applicable in the spleen, we screened for EphA2/ephrin-A1 expression and reexamined the cellular properties of the J774.1 subline. We found that ephrin-A1 was expressed in the vasculature of the marginal zone and the red pulp and that its expression was upregulated in response to phagocyte depletion; further, CD115, F4/80, and CXCR4 were expressed in J774.1 cells, which serve as a usable substitute for monocytes/macrophages. Moreover, following ephrin-A1 stimulation, truncated EphA2 did not detectably interfere with the phosphorylation of endogenous EphA2, and it potentiated cell adhesion possibly through modulation of integrin avidity. Accordingly, by intravenously injecting mice with equal numbers of J774.1 and the subline cells labeled with distinct fluorochromes, we determined that truncated EphA2 markedly potentiated preferential cell infiltration into the red pulp and the marginal zone. Thus, modulation of EphA2 signaling might contribute to effective transplantation of tissue-specific resident macrophages and/or monocytes.