Two widely used anti-DR alpha monoclonal antibodies bind to an intracellular C-terminal epitope

Prognostic significance of myeloid immune cells and their spatial distribution in the colorectal cancer microenvironment

Background

Myeloid cells represent an abundant yet heterogeneous cell population in the colorectal cancer microenvironment, and their roles remain poorly understood.

Methods

We used multiplexed immunofluorescence combined with digital image analysis to identify CD14⁺ monocytic and CD15⁺ granulocytic cells and to evaluate their maturity (HLA-DR and CD33), immunosuppressive potential (ARG1) and proximity to cytokeratin (KRT)-positive tumor cells in 913 colorectal carcinomas. Using covariate data of 4465 incident colorectal cancers in two prospective cohort studies, the inverse probability weighting method was used with multivariable-adjusted Cox proportional hazards models to assess cancer-specific mortality according to ordinal quartiles (Q1–Q4) of myeloid cell densities. Immune cell–tumor cell proximity was measured with the nearest neighbor method and the G-cross function, which determines the likelihood of any tumor cell having at least one immune cell of the specified type within a certain radius.

Results

Higher intraepithelial (P_trend=0.0002; HR for Q4 (vs Q1), 0.48, 95% CI 0.31 to 0.76) and stromal (P_trend <0.0001; HR for Q4 (vs Q1), 0.42, 95% CI 0.29 to 0.63) densities of CD14⁺HLA-DR⁺ cells were associated with lower colorectal cancer-specific mortality while, conversely, higher intraepithelial densities of CD14⁺HLA-DR⁻ cells were associated with higher colorectal cancer-specific mortality (P_trend=0.0003; HR for Q4 (vs Q1), 1.78, 95% CI 1.25 to 2.55). Spatial analyses indicated that CD15⁺ cells were located closer to tumor cells than CD14⁺ cells, and CD14⁺HLA-DR⁺ cells were closer to tumor than CD14⁺HLA-DR⁻ cells (p<0.0001). The G-cross proximity measurement, evaluating the difference in the likelihood of any tumor cell being colocated with at least one CD14⁺HLA-DR⁺ cell versus CD14⁺HLA-DR⁻ cell within a 20 µm radius, was associated with lower colorectal cancer-specific mortality (P_trend <0.0001; HR for Q4 (vs Q1), 0.37, 95% CI 0.24 to 0.57).

Conclusions

Myeloid cell populations occur in spatially distinct distributions and exhibit divergent, subset-specific prognostic significance in colorectal cancer, with mature CD14⁺HLA-DR⁺ and immature CD14⁺HLA-DR⁻ monocytic phenotypes most notably showing opposite associations. These results highlight the prognostic utility of multimarker evaluation of myeloid cell infiltrates and reveal a previously unrecognized degree of spatial organization for myeloid cells in the immune microenvironment.

Microglia in the dorsal raphe nucleus plays a potential role in both suicide facilitation and prevention in affective disorders

An involvement of the central serotonergic system has constantly been reported in the pathogenesis of suicide. The dorsal raphe nucleus (DRN) is the main source of serotonergic innervation of forebrain limbic structures disturbed in suicidal behaviour, in which an abnormal microglia reaction seems to play a role. In our present study, the density of microglia immunostained for the HLA-DR antigen was evaluated in the DRN. These analyses were carried out on paraffin-embedded brains from 24 suicidal and 21 non-suicidal patients; among them, 27 depressed (15 major depressive disorder and 12 bipolar disorder) and 18 schizophrenia (9 residual and 9 paranoid) patients and 22 matched controls without mental disorders. Only the non-suicidal depressed subgroup revealed significantly lower microglial reaction, i.e., a decreased density of HLA-DR positive microglia versus both depressed suicide victims and controls. The effect was not related to antidepressant or antipsychotic medication, as the former correlated positively with microglial density in non-suicidal depressed patients, and the latter had no effect. Moreover, the comparison of these results with previously published data from our workgroup in the same cohort (Krzyżanowska et al. in Psychiatry Res 241:43-46, 4) suggested a positive impact of microglia on ribosomal DNA transcription in DRN neurons in the non-suicidal depressed subgroup, but not in depressed suicidal cases. Therefore, the interaction between microglia and neurons in the DRN may be potentially involved in opposite ways regarding suicide facilitation and prevention in the tested subgroups of depressed patients.

A novel family of human leukocyte antigen class II receptors may have its origin in archaic human species

HLA class II α and β chains form receptors for antigen presentation to CD4(+) T cells. Numerous pairings of class II α and β subunits from the wide range of haplotypes and isotypes may form, but most of these combinations, in particular those produced by isotype mixing, yielded mismatched dimers. It is unclear how selection of functional receptors is achieved. At the atomic level, it is not known which interactions of class II residues regulate selection of matched αβ heterodimers and the evolutionary origin of matched isotype mixed dimer formation. In this study we investigated assembly of isotype-mixed HLA class II α and β heterodimers. Assembly and carbohydrate maturation of various HLA-class II isotype-mixed α and β subunits was dependent on the groove binding section of the invariant chain (Ii). By mutation of polymorphic DPβ sequences, we identified two motifs, Lys-69 and GGPM-(84-87), that are engaged in Ii-dependent assembly of DPβ with DRα. We identified five members of a family of DPβ chains containing Lys-69 and GGPM 84-87, which assemble with DRα. The Lys/GGPM motif is present in the DPβ sequence of the Neanderthal genome, and this ancient sequence is related to the human allele DPB1*0401. By site-directed mutagenesis, we inspected Neanderthal amino acid residues that differ from the DPB1*0401 allele and aimed to determine whether matched heterodimers are formed by assembly of DPβ mutants with DRα. Because the *0401 allele is rare in the sub-Saharan population but frequent in the European population, it may have arisen in modern humans by admixture with Neanderthals in Europe.

Cutting edge: NADPH oxidase modulates MHC class II antigen presentation by B cells

Phagocyte NADPH oxidase plays a key role in pathogen clearance via reactive oxygen species (ROS) production. Defects in oxidase function result in chronic granulomatous disease with hallmark recurrent microbial infections and inflammation. The oxidase's role in the adaptive immune response is not well understood. Class II presentation of cytoplasmic and exogenous Ag to CD4(+) T cells was impaired in human B cells with reduced oxidase p40(phox) subunit expression. Naturally arising mutations, which compromise p40(phox) function in a chronic granulomatous disease patient, also perturbed class II Ag presentation and intracellular ROS production. Reconstitution of patient B cells with a wild-type, but not a mutant, p40(phox) allele restored exogenous Ag presentation and intracellular ROS generation. Remarkably, class II presentation of epitopes from membrane Ag was robust in p40(phox)-deficient B cells. These studies reveal a role for NADPH oxidase and p40(phox) in skewing epitope selection and T cell recognition of self Ag.

Stoichiometry of HLA class II-invariant chain oligomers

BACKGROUND

The HLA gene complex encodes three class II isotypes, DR, DQ, and DP. HLA class II molecules are peptide receptors that present antigens for recognition by T lymphocytes. In antigen presenting cells, the assembly of matched α and β subunits to heterodimers is chaperoned by invariant chain (Ii). Ii forms a homotrimer with three binding sites for class II heterodimers. The current model of class II and Ii structure states that three αβ heterodimers bind to an Ii trimer.

METHODOLOGY/PRINCIPAL FINDINGS

[corrected] We have now analyzed the composition and size of the complexes of class II and Ii using epitope tagged class II subunits and density gradient experiments. We show here that class II-Ii oligomers consist of one class II heterodimer associated with one Ii trimer, such that the DR, DQ and DP isotypes are contained within separate complexes with Ii.

CONCLUSION/SIGNIFICANCE

We propose a structural model of the class II-Ii oligomer and speculate that the pentameric class II-Ii complex is bent towards the cell membrane, inhibiting the binding of additional class II heterodimers to Ii.

LAMP-2-deficient human B cells exhibit altered MHC class II presentation of exogenous antigens

Major histocompatibility complex (MHC) class II molecules present antigenic peptides derived from engulfed exogenous proteins to CD4(+) T cells. Exogenous antigens are processed in mature endosomes and lysosomes where acidic proteases reside and peptide-binding to class II alleles is favoured. Hence, maintenance of the microenvironment within these organelles is probably central to efficient MHC class II-mediated antigen presentation. Lysosome-associated membrane proteins such as LAMP-2 reside in mature endosomes and lysosomes, yet their role in exogenous antigen presentation pathways remains untested. In this study, human B cells lacking LAMP-2 were examined for changes in MHC class II-restricted antigen presentation. MHC class II presentation of exogenous antigen and peptides to CD4(+) T cells was impaired in the LAMP-2-deficient B cells. Peptide-binding to MHC class II on LAMP-2-deficient B cells was reduced at physiological pH compared with wild-type cells. However, peptide-binding and class II-restricted antigen presentation were restored by incubation of LAMP-2-negative B cells at acidic pH, suggesting that efficient loading of exogenous epitopes by MHC class II molecules is dependent upon LAMP-2 expression in B cells. Interestingly, class II presentation of an epitope derived from an endogenous transmembrane protein was detected using LAMP-2-deficient B cells. Consequently, LAMP-2 may control the repertoire of peptides displayed by MHC class II molecules on B cells and influence the balance between endogenous and exogenous antigen presentation.

A new monoclonal antibody recognizing a linear determinant on the HLA-DRalpha chain N-terminus

We report the generation of a monoclonal antibody (MAb) that reacts to the N-terminus of the denatured HLA-DRalpha chain. The 1C4.6 MAb was raised against a peptide corresponding to amino acid residues 10 to 32 of a highly conserved region within the alpha1 domain of HLA-DR. This region partially overlaps with the epitope recognized by the conformationally dependent L243 MAb. In Western blot analysis, MAb 1C4.6 reacted with denatured HLA-DRalpha chains, but failed to bind the HLA-DRbeta chain expressed individually by transfectant cells, confirming that it recognizes an epitope on the alpha-chain of HLA-DR. In addition, this antibody was found to be isotype specific to HLA-DRalpha, as it did not cross-react to HLA class II proteins HLA-DP and-HLA-DQ. The 1C4.6 MAb is a valuable addition to existing reagents used to probe the structure and function of MHC class II molecules. This anti-HLA-DRalpha1 domain MAb may prove valuable for studies of HLA class II heterodimer assembly, structure, and function, as well as for studies into the release of soluble MHC class II.

Immunological aspects in the neurobiology of suicide: elevated microglial density in schizophrenia and depression is associated with suicide

OBJECTIVES

Suicide has a high prevalence in patients with schizophrenia and affective disorder. Our recent postmortem study [Steiner J, Mawrin C, Ziegeler A, Bielau H, Ullrich O, Bernstein HG, Bogerts B. Distribution of HLA-DR-positive microglia in schizophrenia reflects impaired cerebral lateralization. Acta Neuropathologica (Berl) 2006;112:305-16.] revealed increased microglial densities in two schizophrenic patients who had committed suicide. Therefore, the hypothesis of microglial activation during acute psychosis was proposed. Alternatively, "suicide" could be a diagnosis-independent factor leading to microgliosis.

METHODS

To clarify this question, microglial HLA-DR expression was analyzed by immunohistochemistry in the dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex (ACC), mediodorsal thalamus (MD) and hippocampus of 16 schizophrenics, 14 depressed patients with affective disorder and 10 matched controls. A subgroup of six schizophrenics and seven patients with affective disorder who committed suicide was included.

RESULTS

ANOVA revealed no effect of diagnosis on microglial density (DLPFC: P=0.469; ACC: P=0.349; MD: P=0.569; hippocampus: P=0.497). However, significant microgliosis was observed in the DLPFC (P=0.004), ACC (P=0.012) and MD (P=0.004) of suicide patients. A similar trend was seen in the hippocampus (P=0.057).

CONCLUSION

In conclusion, immunological factors may play a hitherto underestimated role in suicide. First, microglial activation might be interpreted as a consequence of presuicidal stress. Second, one might speculate a causal link between microglial activation and suicidal behaviour, such as neuroendocrine factors, cytokines, and nitric oxide, which are released from microglial cells and are known to modulate noradrenergic or serotonergic neurotransmission and thus may trigger suicidality.

Dendritic Cells Sensitize TCRs through Self-MHC-Mediated Src Family Kinase Activation

It is unclear whether peptide-MHC class II (pMHC) complexes on distinct types of APCs differ in their capacity to trigger TCRs. In this study, we show that individual cognate pMHC complexes displayed by dendritic cells (DCs), as compared with nonprofessional APCs, are far better in productively triggering Ag-specific TCRs independently of conventional costimulation. As we further show, this is accomplished by the unique ability of DCs to robustly activate the Src family kinases (SFKs) Lck and Fyn in T cells even in the absence of cognate peptide. Instead, this form of SFK activation depends on interactions of DC-displayed MHC with TCRs of appropriate restriction, suggesting a central role of self-pMHC recognition. DC-mediated SFK activation leads to "TCR licensing," a process that dramatically increases sensitivity and magnitude of the TCR response to cognate pMHC. Thus, TCR licensing, besides costimulation, is a main mechanism of DCs to present Ag effectively.

Circulating, soluble forms of major histocompatability complex antigens are not exosome-associated

In vitro studies have shown that soluble MHC (sMHC) released by cell lines is bound to nano-vesicles termed exosomes. It is thought that exosomes may represent the major reservoir of sMHC class I and II molecules in biological fluids. However, most studies have been confined to in vitro assays performed with cell lines. We show here that sMHC in the serum or plasma differs from exosome-bound sMHC in five ways: In contrast to exosome-associated sMHC, circulating sMHC is of low density, has a low apparent molecular mass (40-300 kDa) and is not detergent-labile. Moreover, the majority of MHC class II isoforms and MHC class I in blood are not physically linked and circulating HLA-DR is accessible to an antibody specific for the HLA-DR alpha-chain intracellular epitope, which is masked by its association with cellular or exosomal membranes. Finally, utilizing transcriptional activator of murine MHC class II (C2ta) promoter-mutant mice, we showed that the release of sMHC class II into the circulation is dependent on the C2ta pI promoter, but not pIII or pIV. This suggests that myeloid dendritic cells and/or macrophages, which preferentially use promoter pI of the C2ta gene, produce most of the sMHC class II found in the circulation.

Thymus development in Macaca fascicularis (Cynomolgus monkey): an approach for toxicology and embryology

Thymus development was studied in the cynomolgus monkey from day 35 of gestation (gd 35) to the stage of advanced involution in a 21-year-old monkey. Special emphasis was placed on thymus cell generation and cellular pattern formation. At gd 35, the epithelial bud of the thymus was visible in a sagittal position at the level of the thoracic aperture. At gd 50, first lymphocyte-like cells and few Human Leukocyte Antigen-D Region (HLA-DR) immunoreactive cells appeared. The cortico-medullary differentiation, Hassall's body precursors and faint immunoreactivity for T-lymphocytes (CD 3-positive) were detected from gd 60 onwards. First macrophages (CD 68 positive) were apparent at day 70, first CD 20 immunoreactive cells (B-lymphocyte-like cells) at gd 85, and natural killer cells (M1014 immunoreactive) at gd 100. At gd 100 all evaluated cell populations present in the adult cynomolgus monkey thymus were in place, whereas no B- and T-cell precursors or (CD 34 and CD 117, respectively) dendritic cells (CD 35 positive cells) were present. All these immunopositive cells persisted, partly with changing distribution patterns, until the advanced age of 21 years with the exception of natural killer cells, which were present only until adult ages (evaluation at 4-7 years). The rationale of this study was to analyse thymic development in the cynomolgus monkey and to evaluate the relevance of the development of thymus in non-human primate as a model for corresponding human targeted toxicological research.

Distribution of HLA-DR-positive microglia in schizophrenia reflects impaired cerebral lateralization

Immunological alterations have been demonstrated in peripheral blood and cerebrospinal fluid of patients with schizophrenia, while previous postmortem studies have provided an inconsistent picture as to the role of microglia in the context of schizophrenia. Microglial activation is a sensitive indicator of changes in the CNS microenvironment, such as inflammatory and neurodegenerative processes. The aim of the present postmortem study was to examine HLA class II (HLA-DR) expression on microglia in brain regions which are particularly relevant for schizophrenia, with regard to hemispheric lateralization. Dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex (ACC), hippocampus and mediodorsal thalamus (MD) were studied in 16 cases with schizophrenia and 16 control subjects. Immunostaining was found in all brain regions and was not restricted to macrophage-like ameboid cells, but also appeared in ramified cells. Region-specific HLA-DR-positive cell density was not significantly different between cases with schizophrenia and controls. However, ameboid microglial cells were lateralized towards the right hemisphere in healthy subjects but not in the schizophrenia group (P=0.01). Postmortem interval correlated with ramified cell numbers in ACC/DLPFC (P=0.01/0.04) and ameboid cell density in hippocampus (P=0.03). Age, gender, duration of disease, medication dosage, storage delay and whole brain volume had no effect. Single case analysis revealed highly elevated microglial cell numbers in ACC and MD of two schizophrenic patients who had committed suicide during acute psychosis. In conclusion, the present data suggest the absence of microgliosis but decreased cerebral lateralization of ameboid microglia in schizophrenia.

Human cytomegalovirus disrupts constitutive MHC class II expression

CD8(+) and CD4(+) T lymphocytes are important in controlling human CMV (HCMV) infection, but the virus has evolved protean mechanisms to inhibit MHC-based Ag presentation and escape T lymphocyte immunosurveillance. Herein, the interaction of HCMV with the MHC class II Ag presentation pathway was investigated in cells stably transfected with class II transactivator. Flow cytometry experiments demonstrate that HCMV infection decreases cell-surface MHC class II expression. HCMV down-regulates MHC class II surface expression without a significant effect on class II RNA or steady-state protein levels. SDS-stability and confocal microscopy experiments demonstrate normal levels of steady-state peptide-loaded class II molecules in infected cells and that class II molecules reach late endosomal and HLA-DM positive peptide-loading compartments. However, MHC class II positive vesicles are retained in an abnormal perinuclear distribution. Finally, experiments with a mutant HCMV strain demonstrate that this novel mechanism of decreased MHC class II expression is not mediated by one of the known HCMV immunomodulatory genes. These defects in MHC class II expression combined with previously identified CMV strategies for decreasing MHC class I expression enables infected cells to evade T lymphocyte immunosurveillance.

In vivo and in vitro modulation of HLA-DM and HLA-DO is induced by B lymphocyte activation

Ag presentation via HLA class II molecules in B lymphocytes depends on the coordinated action of HLA-DM, the catalyst of class II-peptide loading, and HLA-DO, a pH-dependent modulator of DM, the expression of which is almost completely restricted to B lymphocytes. The relative expression levels of both class II modulators are critical for the composition of the HLA class II peptide repertoire. The data in this work demonstrate that DO and DM expression are both dependent on the cellular activation status in primary human B lymphocytes. In vivo low-density activated primary human B lymphocytes show a prominent reduction in DO and DM expression when compared with high-density resting primary B lymphocytes. In vitro, reduction of DO and DM expression can be induced by B lymphocyte activation via the B cell receptor or by use of the phorbol ester, PMA. Specific inhibition of protein kinase C resulted in a significant reduction of HLA-DO and is potentially due to protein degradation in lysosomal compartments as the phenomenon is reversed by chloroquine. Thus, the expression of the dedicated HLA class II chaperone DM and its pH-dependent modulator DO is regulated and tightly controlled by the activation status of the B lymphocyte.

Quantitative relationship between MHC class II-superantigen complexes and the balance of T cell activation versus death

The binding of bacterial superantigens (SAgs) is profoundly affected by the nature of the MHC class II-associated antigenic peptide. It was proposed that this limitation in the density of SAgs displayed at the surface of APCs is important for efficient TCR serial triggering as well as for preventing apoptosis of the responding T lymphocytes. Here, we have addressed quantitatively the size of this SAg-receptive pool of HLA-DR molecules that are available to bind and present staphylococcal enterotoxin A (SEA) at the surface of B lymphocytes. Our binding curves, depletion experiments, and quantitative immunoprecipitations show that about half the HLA-DR class II molecules on B cells are refractory to SEA binding. Yet, as compared with typical nominal Ags, an unusually high amount of class II-SAg complexes can be presented to T cells. This characteristic appears to be necessary for SAg-induced T cell apoptosis. When <0.3% of the total cell surface MHC class II molecules are occupied by SEA, T cells undergo a normal sequence of early activation events. However, presentation of a ligand density beyond this threshold results in T cell activation that is readily aborted by apoptosis but only after a few cell divisions. Thus, we confirm the existence of MHC class II subsets that are structurally unable to present SEA and provide a quantitative framework to account for the ability of bacterial SAgs to induce peripheral activation vs tolerance in the host.

Cellular distribution of a mixed MHC class II heterodimer between DRalpha and a chimeric DObeta chain

Human MHC class II antigens include HLA-DR, -DQ, and -DP molecules that present antigens to CD4+ T cells, as well as the non-classical molecules HLA-DM and -DO. HLA-DM promotes peptide binding to class II molecules in endocytic compartments and HLA-DO, which is physically associated with HLA-DM in B lymphocytes, regulates HLA-DM function. Antibodies specific for the DObeta chain were obtained by immunization of mice with a heterodimer consisting of a chimeric DObeta chain (DR/DObeta), containing 18 N-terminal residues of DRbeta, paired with the DRalpha chain and isolated from transfected murine fibroblasts. The specificity of this serum for the DObeta chain and the lysosomal expression of the HLA-DO protein was confirmed using mutant human B cell lines lacking DR or DO molecules. The lysosomal localization of HLA-DO in human B cells contrasts with the cell surface expression of the mixed pair in transfected murine fibroblasts and raises questions concerning the role of the putative targeting motifs in HLA-DO. Transfection of the chimeric DR/DObeta chain along with DRalpha into human epithelial HeLa cells resulted in high levels of expression of the mixed isotypic pair at the surface of transfectants as well as in lysosomes. The same pattern was observed in HeLa cells transfected with the DObeta chimera and a DRa chain lacking the cytoplasmic tail. Taken together, these results suggest that functional sorting motifs exist in the DObeta chain but that the tight compartmentalization of HLA-DO observed inside B lymphocytes is controlled by the HLA-DOalpha chain and HLA-DM.