PECAM is a molecule used specifically during the diapedesis step when neutrophils and monocytes leave the blood compartment. Anti-PECAM reagents, such as Abs and soluble fusion proteins, block diapedesis both in vivo and in vitro. However, the PECAM knockout mouse in C57BL/6 strain has no serious defects in most models of inflammation. We show in this study that the same PECAM knockout backcrossed into the FVB/n strain clearly has reduced leukocyte emigration in two models of inflammation. Furthermore, we show that anti-PECAM reagents can block leukocyte emigration in several other wild-type strains of mice like FVB/n, SJL, and the outbred strain Swiss Webster. This clearly shows that the C57BL/6 strain is uniquely able to compensate for the loss of PECAM function. Murine models of inflammatory disease that have been studied using C57BL/6 mice should be re-evaluated using FVB/n or other mouse strains to determine whether PECAM plays a role in those models.

Platelet Endothelial Cell Adhesion Molecule (PECAM) is an adhesion and signaling molecule used for leukocyte extravasation. We have generated two strains of PECAM-deficient mouse, one in the original C57BL/6 and a second by backcrossing nice generations into the FVB/n strain. The FVB/n strain has reduced responses in models of acute inflammation. We show here that this strain is also susceptible to a chronic pneumonia which leads to pulmonary fibrosis. In contrast, PECAM-deficient C57BL/6 mice do not develop this lung disease and have normal responses in acute models of inflammation. This demonstrates that PECAM-dependent and -independent mechanisms are found in both acute and chronic inflammation. Further, the PECAM-deficient FVB/n strain has many pathologic similarities to the human disease Idiopathic Pulmonary Fibrosis, suggesting that similar molecular mechanisms may play a role in human disease.

CD99, a glycoprotein found on the surfaces of leukocytes and concentrated at the borders of endothelial cells, plays a major role in the migration of leukocytes across endothelial cells into sites of inflammation, and has other roles in thymocyte development. The human and mouse genomes encode only two proteins related to CD99. One of these, XGA, is a red blood cell surface antigen. The function of the other, CD99-like 2 (CD99L2), is not known. We cloned mouse CD99L2 and used CD99L2 isolated from transfected cells to raise specific antibodies. Similar to human CD99, CD99L2 was expressed at the borders between transfected cells as well as on mouse leukocytes and vascular endothelial cells in situ. Transfection of L cell fibroblasts with CD99L2 imparted to them the ability to adhere to each other in a divalent cation-dependent, homophilic manner. Anti-CD99L2 antibody blocked influx of neutrophils and monocytes into a site of inflammation in vivo.

BackgroundPrevious studies have demonstrated that knockout or inhibition of Platelet/Endothelial Cell Adhesion Molecule (PECAM, CD31) in a number of murine strains results in impaired inflammatory responses, but that no such phenotype is seen in the C57BL/6 (B6) murine background.Methodology/Principal FindingsWe have undertaken a quantitative trait locus (QTL) mapping effort between FVB/n (FVB) and B6 mice deficient for PECAM to identify the gene or genes responsible for this unique feature of B6 mice. We have identified a locus on murine chromosome 2 at approximately 35.8 Mb that is strongly associated (LOD score = 9.0) with inflammatory responses in the absence of PECAM.Conclusions/SignificanceThese data potentiate further study of the diapedesis machinery, as well as potential identification of new components of this machinery. As such, this study is an important step to better understanding the processes of inflammation.

Vaccine efficacy depends on strong long-term development of immune memory and the formation of memory CD8+ T cells is critical for recall responses to infection. Upon antigen recognition by naïve T cells, the strength of the TcR signal influences the subsequent effector and memory cells differentiation. Here, we have examined the role of Itk, a tyrosine kinase critical for TcR signaling, in CD8+ effector and memory T cell differentiation during Listeria monocytogenes infection. We found that the reduced TcR signal strength in Itk deficient naïve CD8+ T cells enhances the generation of memory T cells during infection. This is accompanied by increased early Eomesodermin, IL-7Rα expression and memory precursor effector cells. Furthermore, Itk is required for optimal cytokine production in responding primary effector cells, but not secondary memory responses. Our data suggests that Itk-mediated signals control the expression of Eomesodermin and IL-7Rα, thus regulating the development of memory CD8+ T cells, but not subsequent response of memory cells.