The role of b2-integrins for the effector functions of polymorphonuclear granulocytes

Background: b2-integrins are heterodimeric surface receptors that are expressed specifically by leukocytes and consist of a variable a (CD11a-d) and a common b-subunit (CD18). Functional impairment of CD18, which causes leukocyte adhesion deficiency type-1 results in an immunocompromised state characterized by severe infections, such as invasive pulmonary aspergillosis (IPA). The underlying immune defects have largely been attributed to an impaired migratory and phagocytic activity of polymorphonuclear granulocytes (PMN). However, the exact contribution of b2-integrins for PMN functions in-vivo has not been elucidated yet, since the mouse models available so far display a constitutive CD18 knockout (CD18-/- or CD18hypo). To determine the PMN-specific role of b2-integrins for innate effector functions and pathogen control, we generated a mouse line with a Ly6G-specific knockdown of the common b-subunit (CD18DLy6G). Methods: We analyzed expression levels of genes implicated in b2-integrin signaling for treated and untreated PMN derived from CD18DLy6G mice and CD18fl/fl mice using RNA-Sequencing. To determine the most up- or downregulated genes, genes were sorted on the basis of log2 [fold change] maximum-likelihood estimation, and the P-value cut-off was set to 0.05. Results were illustrated using the pheatmap package. Functional interaction networks were visualized using the STRING package in the open-source platform Cytoscape. Results: Our results revealed a downregulation of b2-integrins , while genes implicated in NFkB singaling were upregulated. With regard to PMN effector function, we observed a downregulation of genes implicated in PMN chemotaxis and microbicidal functions such as Defb40. We isolated PMN from bone marrow of CD18fl/fl and CD18DLy6G mice (n=3). Each 10^6 PMN were either lysed directly after isolation or cultured overnight with GM-CSF (10ng/ml) plus LPS (1µg/ml). Subsequently RNA was purified and quantified with a Qubit fluorometer in order to compare genotype-dependent expression levels both for untreated and treated conditions.