Tolerizing mice to human leukocytes: a step toward the production of monoclonal antibodies specific for human dendritic cells

Tolerization as a tool for generating novel monoclonal antibodies

Standard hybridoma production involves the fusion of spleen cells from an immunized mouse with a non-secretory murine myeloma cell line. While this technology has provided numerous reagents that are highly valuable, demand is now increasing for monoclonal antibodies which can distinguish between closely related antigens. Induction of tolerance towards common antigens enables the recovery of high-specificity reagents that have previously proved elusive. This review details a number of strategies using either complex protein mixtures or purified proteins as tolerogens and subsequent immunization with a closely related immunogen.

BDCA-2, BDCA-3, and BDCA-4: three markers for distinct subsets of dendritic cells in human peripheral blood

We have generated a panel of mAbs that identify three presumably novel human dendritic cell Ags: BDCA-2, BDCA-3, and BDCA-4. In blood, BDCA-2 and BDCA-4 are expressed on CD11c(-) CD123(bright) plasmacytoid dendritic cells, whereas BDCA-3 is expressed on small population of CD11c(+) CD123(-) dendritic cells. All three Ags are not detectable on a third blood dendritic cell population, which is CD1c(+) CD11c(bright) CD123(dim), or on any other cells in blood. BDCA-4 is also expressed on monocyte-derived and CD34(+) cell-derived dendritic cells. Expression of all three Ags dramatically changes once blood dendritic cells undergo in vitro maturation. BDCA-2 is completely down-regulated on plasmacytoid CD11c(-) CD123(bright) dendritic cells, expression of BDCA-3 is up-regulated on both plasmacytoid CD11c(-) CD123(bright) dendritic cells and CD1c(+) CD11c(bright) CD123(dim) dendritic cells, and expression of BDCA-4 is up-regulated on CD1c(+) CD11c(bright) CD123(dim) dendritic cells. BDCA-2 is rapidly internalized at 37 degrees C after mAb labeling. The three presumably novel Ags serve as specific markers for the respective subpopulations of blood dendritic cells in fresh blood and will be of great value for their further analysis and to evaluate their therapeutic potential.

Can Langerhans cell UV injury and dendritic cell infection by immunosuppressive viruses induce immunologic tolerance? First part

Though it has not been described by the HIV1-AIDS consensual thinkers, we propose the thesis according to which some immunocyte populations or their interactions can achieve tolerance or split immunologic tolerance in patients suffering from this disease. The proposed concept is based on data registered: 1) after Langerhans cell local injury by UV irradiation in their physiologic localisations, the skin and mucosae: and 2) after systemic infections of dendritic cells by immunosuppressive viruses, including some animal retroviruses, measles, lymphocytic choriomeningitis viruses, and HIV1. We can describe both types or manifestations concerning local UV injury and systemic viral infection combined in an AIDS patient, who received a PUVA irradiation before and at the beginning of his virostatic treatment, which he has now successfully received for eight years. The conditions of this patient differ from those of non-UV victim patients of the cohort to which he belongs, for two reasons: 1) the numbers of both his CD4+ and his suppressor T cells have been reduced to near 0 after UV irradiation; and b) his viral load, which has been exponentially reduced, has not reached, after eight years, the asymptotic part of the VL curve, characterized by PCR non-assessable viral load, which the non-UV victims of the cohort have reached. We wonder if, in this patient, there do not coexist two sorts of immunologic phenomena: 1) one bound to CTL, the numbers of which are increased, whose cytotoxicity is added to the virostatic action; and 2) one bound to the virus attack restriction by an immunologic tolerance. Contrary to the cohort controls, in whom an allogenic skin graft was only accepted for 20 days, the graft of the same donor has been tolerated in the UV victim patient for 70 days. This patient will be discussed in the second part of this editorial: the first part is devoted to the description of several conditions in which Langerhans cell injury by UV, or dendritic cell infections by measles, lymphocytic choriomeningitis viruses or animal retroviruses are followed, not only by immunodepression manifestations, but by immunologic tolerance.

Extensive characterization of the immunophenotype and pattern of cytokine production by distinct subpopulations of normal human peripheral blood MHC II+/lineage- cells

Dendritic cells (DC) represent the most powerful professional antigen-presenting cells (APC) in the immune system. The aim of the present study was to analyse, on a single-cell basis by multiparametric flow cytometry with simultaneous four-colour staining and a two-step acquisition procedure, the immunophenotypic profile and cytokine production of DC from 67 normal whole peripheral blood (PB) samples. Two clearly different subsets of HLA-II+/lineage- were identified on the basis of their distinct phenotypic characteristics: one DC subset was CD33strong+ and CD123dim+ (0.16 +/- 0.06% of the PB nucleated cells and 55.9 +/- 11. 9% of all PB DC) and the other, CD33dim+ and CD123strong+ (0.12 +/- 0.04% of PB nucleated cells and 44.53 +/- 11.5% of all PB DC). Moreover, the former DC subpopulation clearly showed higher expression of the CD13 myeloid-associated antigen, the CD29 and CD58 adhesion molecules, the CD2, CD5 and CD86 costimulatory molecules, the CD32 IgG receptor and the CD11c complement receptor. In addition, these cells showed stronger HLA-DR and HLA-DQ expression and a higher reactivity for the IL-6 receptor alpha-chain (CD126) and for CD38. In contrast, the CD123strong+/CD33dim+ DC showed a stronger reactivity for the CD4 and CD45RA molecules, whereas they did not express the CD58, CD5, CD11c and CD13 antigens. Regarding cytokine production, our results show that while the CD33strong+/CD123dim+ DC are able to produce significant amounts of inflammatory cytokines, such as IL-1beta (97 +/- 5% of positive cells), IL-6 (96 +/- 1.1% of positive cells), IL-12 (81.5 +/- 15.5% of positive cells) and tumour necrosis factor-alpha (TNF-alpha) (84 +/- 22.1% of positive cells) as well as chemokines such as IL-8 (99 +/- 1% of positive cells), the functional ability of the CD123strong+/CD33dim+ DC subset to produce cytokines under the same conditions was almost null. Our results therefore clearly show the presence of two distinct subsets of DC in normal human PB, which differ not only in their immunophenotype but also in their functionality, as regards cytokine production.

Bacterial lipopolysaccharide contamination of commercial collagen preparations may mediate dendritic cell maturation in culture

Dendritic cells (DC) are potent antigen presenting cells, which are responsible for the initiation of naive T and T-dependent immune responses. The present studies were based upon recent reports that commercial collagen I preparations induce the maturation of human DC in vitro. We show that human blood monocyte-derived (GM-CSF and IL-4 cultured) DC pulsed on collagen I-coated plates undergo a dose-dependent increase in stimulatory capacity in oxidative mitogenesis assays. This is accompanied by the upregulation of costimulatory molecules (CD40, CD80, CD86), CD25, ICAM-1 and the DC-specific marker CD83. The maturation effect is more potent than TNF-alpha, which is a known mediator of DC function. However, bacterial lipopolysaccharide (LPS), a powerful inducer of DC maturation, was found to be present at very high levels in one commercial collagen solution that was tested. The effect of LPS upon DC maturation was similar to culture with collagen. Furthermore, a different collagen I preparation with low levels of LPS contamination was less effective at inducing DC maturation, while spiking the collagen solution with LPS prior to plastic coating equalised these effects. Finally, human monocyte-derived DC were found not to express typical collagen receptors VLA-1, 2 and 3. We therefore propose that LPS contamination may at least partially explain reported collagen I induced DC maturation.