Complement-Opsonized Nano-Carriers Are Bound by Dendritic Cells (DC) via Complement Receptor (CR)3, and by B Cell Subpopulations via CR-1/2, and Affect the Activation of DC and B-1 Cells.

The development of nanocarriers (NC) for biomedical applications has gained large interest due to their potential to co-deliver drugs in a cell-type-targeting manner. However, depending on their surface characteristics, NC accumulate serum factors, termed protein corona, which may affect their cellular binding. We have previously shown that NC coated with carbohydrates to enable biocompatibility triggered the lectin-dependent complement pathway, resulting in enhanced binding to B cells via complement receptor (CR)1/2. Here we show that such NC also engaged all types of splenic leukocytes known to express CR3 at a high rate when NC were pre-incubated with native mouse serum resulting in complement opsonization. By focusing on dendritic cells (DC) as an important antigen-presenting cell type, we show that CR3 was essential for binding/uptake of complement-opsonized NC, whereas CR4, which in mouse is specifically expressed by DC, played no role. Further, a minor B cell subpopulation (B-1), which is important for first-line pathogen responses, and co-expressed CR1/2 and CR3, in general, engaged NC to a much higher extent than normal B cells. Here, we identified CR-1/2 as necessary for binding of complement-opsonized NC, whereas CR3 was dispensable. Interestingly, the binding of complement-opsonized NC to both DC and B-1 cells affected the expression of activation markers. Our findings may have important implications for the design of nano-vaccines against infectious diseases, which codeliver pathogen-specific protein antigen and adjuvant, aimed to induce a broad adaptive cellular and humoral immune response by inducing cytotoxic T lymphocytes that kill infected cells and pathogen-neutralizing antibodies, respectively. Decoration of nano-vaccines either with carbohydrates to trigger complement activation in vivo or with active complement may result in concomitant targeting of DC and B cells and thereby may strongly enhance the extent of dual cellular/humoral immune responses.

ß2 Integrins-Multi-Functional Leukocyte Receptors in Health and Disease.

ß2 integrins are heterodimeric surface receptors composed of a variable α (CD11a-CD11d) and a constant ß (CD18) subunit and are specifically expressed by leukocytes. The α subunit defines the individual functional properties of the corresponding ß2 integrin, but all ß2 integrins show functional overlap. They mediate adhesion to other cells and to components of the extracellular matrix (ECM), orchestrate uptake of extracellular material like complement-opsonized pathogens, control cytoskeletal organization, and modulate cell signaling. This review aims to delineate the tremendous role of ß2 integrins for immune functions as exemplified by the phenotype of LAD-I (leukocyte adhesion deficiency 1) patients that suffer from strong recurrent infections. These immune defects have been largely attributed to impaired migratory and phagocytic properties of polymorphonuclear granulocytes. The molecular base for this inherited disease is a functional impairment of ß2 integrins due to mutations within the CD18 gene. LAD-I patients are also predisposed for autoimmune diseases. In agreement, polymorphisms within the CD11b gene have been associated with autoimmunity. Consequently, ß2 integrins have received growing interest as targets in the treatment of autoimmune diseases. Moreover, ß2 integrin activity on leukocytes has been implicated in tumor development.

Neutrophil-Specific Knockdown of ß2 Integrins Impairs Antifungal Effector Functions and Aggravates the Course of Invasive Pulmonal Aspergillosis.

ß2-integrins are heterodimeric surface receptors that are expressed specifically by leukocytes and consist of a variable α (CD11a-d) and a common ß-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 ß2-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 ß2-integrins for innate effector functions and pathogen control, we generated a mouse line with a Ly6G-specific knockdown of the common ß-subunit (CD18Ly6G cKO). We characterized CD18Ly6G cKO mice in-vitro to confirm the PMN-specific knockdown of ß2-integrins. Next, we investigated the clinical course of IPA in A. fumigatus infected CD18Ly6G cKO mice with regard to the fungal burden, pulmonary inflammation and PMN response towards A. fumigatus. Our results revealed that the ß2-integrin knockdown was restricted to PMN and that CD18Ly6G cKO mice showed an aggravated course of IPA. In accordance, we observed a higher fungal burden and lower levels of proinflammatory innate cytokines, such as TNF-α, in lungs of IPA-infected CD18Ly6G cKO mice. Bronchoalveolar lavage revealed higher levels of CXCL1, a stronger PMN-infiltration, but concomitantly elevated apoptosis of PMN in lungs of CD18Ly6G cKO mice. Ex-vivo analysis further unveiled a strong impairment of PMN effector function, as reflected by an attenuated phagocytic activity, and a diminished generation of reactive oxygen species (ROS) and neutrophil-extracellular traps (NET) in CD18-deficient PMN. Overall, our study demonstrates that ß2-integrins are required specifically for PMN effector functions and contribute to the clearance of A. fumigatus by infiltrating PMN, and the establishment of an inflammatory microenvironment in infected lungs.

Impaired Treg-DC interactions contribute to autoimmunity in leukocyte adhesion deficiency type 1.

Leukocyte adhesion deficiency type 1 (LAD-1) is a rare disease resulting from mutations in the gene encoding for the common ß-chain of the ß2-integrin family (CD18). The most prominent clinical symptoms are profound leukocytosis and high susceptibility to infections. Patients with LAD-1 are prone to develop autoimmune diseases, but the molecular and cellular mechanisms that result in coexisting immunodeficiency and autoimmunity are still unresolved. CD4+FOXP3+ Treg are known for their essential role in preventing autoimmunity. To understand the role of Treg in LAD-1 development and manifestation of autoimmunity, we generated mice specifically lacking CD18 on Treg (CD18Foxp3), resulting in defective LFA-1 expression. Here, we demonstrate a crucial role of LFA-1 on Treg to maintain immune homeostasis by modifying T cell-DC interactions and CD4+ T cell activation. Treg-specific CD18 deletion did not impair Treg migration into extralymphatic organs, but it resulted in shorter interactions of Treg with DC. In vivo, CD18Foxp3 mice developed spontaneous hyperplasia in lymphatic organs and diffuse inflammation of the skin and in multiple internal organs. Thus, LFA-1 on Treg is required for the maintenance of immune homeostasis.

ß2 Integrins on Dendritic Cells Modulate Cytokine Signaling and Inflammation-Associated Gene Expression, and Are Required for Induction of Autoimmune Encephalomyelitis.

Heterodimeric ß2 integrin surface receptors (CD11a-d/CD18) are specifically expressed by leukocytes that contribute to pathogen uptake, cell migration, immunological synapse formation and cell signaling. In humans, the loss of CD18 expression results in leukocyte adhesion deficiency syndrome (LAD-)1, largely characterized by recurrent severe infections. All available mouse models display the constitutive and ubiquitous knockout of either α or the common ß2 (CD18) subunit, which hampers the analysis of the cell type-specific role of ß2 integrins in vivo. To overcome this limitation, we generated a CD18 gene floxed mouse strain. Offspring generated from crossing with CD11c-Cre mice displayed the efficient knockdown of ß2 integrins, specifically in dendritic cells (DCs). Stimulated ß2-integrin-deficient splenic DCs showed enhanced cytokine production and the concomitantly elevated activity of signal transducers and activators of transcription (STAT) 1, 3 and 5, as well as the impaired expression of suppressor of cytokine signaling (SOCS) 2-6 as assessed in bone marrow-derived (BM) DCs. Paradoxically, these BMDCs also showed the attenuated expression of genes involved in inflammatory signaling. In line, in experimental autoimmune encephalomyelitis mice with a conditional DC-specific ß2 integrin knockdown presented with a delayed onset and milder course of disease, associated with lower frequencies of T helper cell populations (Th)1/Th17 in the inflamed spinal cord. Altogether, our mouse model may prove to be a valuable tool to study the leukocyte-specific functions of ß2 integrins in vivo.

Toward anticancer immunotherapeutics: well-defined polymer-antibody conjugates for selective dendritic cell targeting.

This paper describes the synthesis of semitelechelic maleimide-modified N-(2-hydroxypropyl)methacrylamid) (HPMA) based polymers of narrow dispersity that can be conjugated e.g. to anti-DEC-205 antibodies affording "star-like" topologies (one antibody decorated with several polymer chains). FCS revealed a hydrodynamic diameter of R(h) = 7.9 nm and SEC narrow dispersity (1.45). Primary in vitro studies with bone marrow derived dendritic cells (DC) show higher cellular binding and uptake rates compared to control samples. Moreover, incubating these conjugates to primary splenocytes demonstrates a much higher affinity to the primary DCs than to any other immune cell population within the spleen. This differentiation is, thereby, much more pronounced for the star-like conjugates than for conjugates made from polymers statistically modified with anti-DEC-205.