Georg M. Sprinzl

Detachment of Human Immunodeficiency Virus Type 1 from Germinal Centers by Blocking Complement Receptor Type 2

ABSTRACT After the transition from the acute to the chronic phase of human immunodeficiency virus (HIV) infection, complement mediates long-term storage of virions in germinal centers (GC) of lymphoid tissue. The contribution of particular complement receptors (CRs) to virus trapping in GC was studied on tonsillar specimens from HIV-infected individuals. CR2 (CD21) was identified as the main binding site for HIV in GC. Monoclonal antibodies (MAb) blocking the CR2-C3d interaction were shown to detach 62 to 77% of HIV type 1 from tonsillar cells of an individual in the presymptomatic stage. Although they did so at a lower efficiency, these antibodies were able to remove HIV from tonsillar cells of patients under highly active antiretroviral therapy, suggesting that the C3d-CR2 interaction remains a primary entrapment mechanism in treated patients as well. In contrast, removal of HIV was not observed with MAb blocking CR1 or CR3. Thus, targeting CR2 may facilitate new approaches toward a reduction of residual virus in GC.

Phagocytosis and Killing of Bacteria by Professional Phagocytes and Dendritic Cells

ABSTRACT Dendritic cells (DC) represent a class of professional antigen-presenting cells whose primary function is to alert the immune system, not to clear invading microorganisms. The objective of our study was to compare the abilities of polymorphonuclear neutrophilic leukocytes (PMN), monocytes, monocyte-derived macrophages (MDM), monocyte-derived immature DC (imDC), and mature DC (maDC) to ingest and destroy Staphylococcus aureus and Escherichia coli. Acridine orange staining and fluorescence microscopy demonstrated that MDM, followed by monocytes, imDC, and PMN, internalized bacteria well but that maDC exhibited less pronounced phagocytic activity. PMN, monocytes, and MDM exhibited a much higher capacity to kill ingested bacteria than both imDC and maDC. In summary, these data are in agreement with the generally accepted idea that different types of leukocytes fulfill specialized tasks in antigen presentation and killing of pathogens.

Cross-Linking of CD32 Induces Maturation of Human Monocyte-Derived Dendritic Cells Via NF-κB Signaling Pathway

Dendritic cells (DC) represent a unique set of APCs that initiate immune responses through priming of naive T cells. Maturation of DC is a crucial step during Ag presentation and can be induced by triggering a broad spectrum of DC surface receptors. Although human DC express several receptors for the Fc portion of IgG which were described to play an important role in Ag internalization, little is known about the effects of IgG or immune complexes on DC maturation. In this study, we show that cross-linking of FcγR-type II (CD32) with immobilized IgG (imIgG) can induce maturation of human monocyte-derived DC via the NF-κB signaling pathway. IgG-mediated maturation was accompanied by a moderate increase of IL-10 secretion, whereas no IL-12 production was observed. Involvement of CD32 was further supported by experiments with the anti-CD32 mAb, which blocked IgG-triggered DC maturation and cytokine secretion significantly. Furthermore, DC cultivated in the presence of imIgG induced allogeneic T cell proliferation. Because this imIgG-induced maturation was considerably impaired in monocyte-derived DC from systemic lupus erythematosus patients, we suggest that DC, which matured in the presence of immune complexes, may contribute to prevention of pathological immune responses.

Factor I-Mediated Processing of Complement Fragments on HIV Immune Complexes Targets HIV to CR2-Expressing B Cells and Facilitates B Cell-Mediated Transmission of Opsonized HIV to T Cells

Our study demonstrates that binding of complement-opsonized HIV to complement receptor type 1 on human erythrocytes (E) via C3b fragments is followed by a rapid normal human serum-mediated detachment of HIV from E. The release was dependent on the presence of factor I indicating a conversion of C3b fragments to iC3b and C3d on the viral surface. This in turn resulted in an efficient binding of opsonized HIV to CR2-expressing B cells, thus facilitating B cell-mediated transmission of HIV to T cells. These data provide a new dynamic view of complement opsonization of HIV, suggesting that association of virus with E might be a transient phenomenon and the factor I-mediated processing of C3b to iC3b and C3d on HIV targets the virus to complement receptor type 2-expressing cells. Thus, factor I in concert with CR1 on E and factor H in serum due to their cofactor activity are likely to be important contributors for the generation of C3d-opsonized infectious HIV reservoirs on follicular dendritic cells and/or B cells in HIV-infected individuals.

B Cell-Mediated Infection of Stimulated and Unstimulated Autologous T Lymphocytes with HIV-l: Role of Complement

In vivo, human immunodeficiency virus type 1 (HIV-1) is opsonized with complement fragments and virus-specific antibodies (Ab). Thus, HIV is able to interact with complement receptor (CR) - and Fc receptor (FcR) - positive cells such as B cells, follicular dendritic cells or macrophages. In this study we demonstrate that the interaction between B cells and HIV has an impact on autologous primary T cell infection in vitro. We confirmed the presence of complement-fragments and virus-specific Ab on serum-treated HIV using a virus-capture assay. In experiments with CR2-specific Ab we showed that the virus/B cell interaction was mainly dependent on CR2. In infection experiments immobilisation of HIV on stimulated tonsil B cells greatly enhanced the infection of interleukin (IL)-2-activated autologous tonsil T cells. Surprisingly, enhancement of T cell infection by B cell-HIV complexes was observed even in the absence of mitogenic stimuli such as PMA and was independent of the addition of exogenous IL-2. Taken together, these results indicate that primary B cells are able to efficiently transmit opsonised HIV to autologous primary T cells and induce a massive enhancement of infection. These in vitro experiments mimic the in vivo situation in the lymphoid tissue and suggest an alternative mechanism for the infection of primary T cells.

Immunosuppressive effects of soluble factors secreted by head and neck squamous cell carcinoma on dendritic cells and T lymphocytes

Recent observations suggest that the inability of the immune system to mount an effective immune response against head and neck squamous cell carcinoma (HNSCC) could be a result of the immunosuppression mediated through soluble factors that are secreted by tumour cells. Therefore, we investigated the effects of conditioned medium obtained from cultures of HNSCC cell lines (HNSCC-CM) on the function of dendritic cells (DC) and T cell immune response. In our study, we could not observe any inhibitory effect of HNSCC-CM on the maturation and the cytokine secretion pattern of DC. On the contrary, HNSCC-CM from two of three cell lines consistently decreased the quantity of IFN-gamma- and IL-4-secreting T cells upon restimulation in vitro. In conclusion, our data suggest that soluble factors secreted by HNSCC cells directly inhibit the function of effector T cells, rather than impeding the process of antigen presentation.

Dendritic Cells in Precancerous Lesions of the Larynx

Objectives: Hyperplastic lesions of the laryngeal mucosa can eventually develop into squamous cell carcinoma. The relationship between dendritic cell infiltration of head and neck cancers and prognosis is well known. Surprisingly, data regarding dendritic cell infiltration in precancerous lesions are not available today. It was the purpose of our study to extend these observations and to investigate in more detail the density and distribution of dendritic cells in precancerous lesions.

Plastination of the larynx for whole-organ sectioning

Whole-organ sectioning is an important technique for the assessment of laryngeal pathology. Since currently established methods require prior decalcification which causes morphological changes, the critical border area between cartilage and surrounding soft tissue cannot be investigated in the same specimen and morphometric studies are not possible. Plastination is a laboratory technique that has previously demonstrated its capacity to overcome these shortcomings. In so doing water and lipids are replaced by curable polymer within the laryngeal cells making decalcification unnecessary. In the present study, more than 50 human larynges were processed using block plastination (BP) and sheet plastination (SP). For BP the complete organ was plastinated as a whole and then cut into thin serial sections. For SP the fresh organ was sliced first and plastinated in a second step. Findings demonstrated that SP allowed for the production of whole-organ sections within a period of 1 week only. Section thicknesses were as thin as 15 mm using a diamond wire saw and an ultramilling device. Sectioning was possible in both coronary and horizontal planes. Following BP, specimens were cut in an industrial cutting machine to thicknesses of about 0.6 mm. Shrinkage of tissue was less than 10% for both methods. In all, SP was technically superior to routine paraffin histology, although cutting equipment is very expensive and delicate in handling. At present the technique of BP is the method of choice for macromorphometrical investigations on serial sections of the human larynx.