Marginal zone macrophages and their role in the immune response against T-independent type 2 antigens: modulation of the cells with specific antibody

Marginal zone macrophages are strategically positioned in the marginal zone of the spleen and are thought to play an important role in the initiation of the immune response to T-independent type 2 responses. The cells are characterized by high phagocytic activity and by the selective uptake of neutral polysaccharides. In the mouse marginal zone macrophages react specifically with the monoclonal antibody ER-TR9. Injection of the antibody resulted in a complete abrogation of the uptake of neutral polysaccharides by the cells in vivo, although the cells were still capable of taking up latex and carbon particles. The complete blockade of the polysaccharide uptake did not result in an altered humoral immune response against this antigen. When the antibody ER-TR9 was coupled to the toxin gelonin a complete elimination of the marginal zone macrophages could be established in vivo. However, complete elimination did not result in changes of the immune responses against 2,4,6-trinitrophenylated Ficoll, suggesting that the marginal zone macrophages are either not involved in this type of response, or that their function can be taken over by other cells. The possible role of these cells and the importance of the spleen in the immune response against bacterial antigens is discussed.     

Modulation of brain hemichannels and gap junction channels by pro-inflammatory agents and their possible role in neurodegeneration

In normal brain, neurons, astrocytes, and oligodendrocytes, the most abundant and active cells express pannexins and connexins, protein subunits of two families forming membrane channels. Most available evidence indicates that in mammals endogenously expressed pannexins form only hemichannels and connexins form both gap junction channels and hemichannels. Whereas gap junction channels connect the cytoplasm of contacting cells and coordinate electric and metabolic activity, hemichannels communicate the intra- and extracellular compartments and serve as a diffusional pathway for ions and small molecules. A subthreshold stimulation by acute pathological threatening conditions (e.g., global ischemia subthreshold for cell death) enhances neuronal Cx36 and glial Cx43 hemichannel activity, favoring ATP release and generation of preconditioning. If the stimulus is sufficiently deleterious, microglia become overactivated and release bioactive molecules that increase the activity of hemichannels and reduce gap junctional communication in astroglial networks, depriving neurons of astrocytic protective functions, and further reducing neuronal viability. Continuous glial activation triggered by low levels of anomalous proteins expressed in several neurodegenerative diseases induce glial hemichannel and gap junction channel disorders similar to those of acute inflammatory responses triggered by ischemia or infectious diseases. These changes are likely to occur in diverse cell types of the CNS and contribute to neurodegeneration during inflammatory process.     

Spontaneous arterial lesions: their possible role in arteriosclerosis

Spontaneous lesions of the arterial wall involving the internal elastic lamellae and variable amounts of the intima are described in the spontaneously hypertensive rat caudal, renal, and mesenteric arteries. A simple model for producing similar circumferential lesions in rat and rabbit carotid arteries has been developed and the subsequent repair of these lesions is described. Two types of circumferential lesion can be produced by the application of 50-160 g of longitudinally applied tension. Small lesions can be up to 400 micron in length and are characterized by the loss of a small area of endothelium and rupture of the internal elastic lamellae. No demonstrable damage to the media is detected in these lesions. Larger lesions can be up to 1 mm in length and are characterized by the loss of endothelium and rupture of the internal as well as a variable number of medial elastic lamellae. Little, if any, damage to the medial smooth muscle cells is observed although the extracellular matrix is often disrupted. Small lesions are completely reendothelialized within 24 hr and larger lesions within 7-10 days. Both large and small lesions repair without the formation of an intimal thickening of smooth muscle cells, despite quite marked damage to the media of the larger lesions.     

Marginal zone of the murine spleen in autotransplants: functional and histological observations in the response against a thymus-independent type 2 antigen.

Splenic tissue from mice was autotransplanted; after initial necrosis, a rapid restoration of implants into a structure histologically indistinguishable from splenic tissue was observed. The development of the marginal zone in these autotransplants, as determined with monoclonal antibodies against different splenic cell types and routine histological stains, was compared with the local and systemic response against a thymus-independent (TI) type 2 antigen. Full restoration of time course and peak of anti-trinitrophenyl (TNP) serum titres against TNP-Ficoll was observed at 4 weeks after autotransplantation. Anti-TNP antibody-forming cells were observed in subnormal and normal numbers in 2- and 4-week old autotransplants, respectively. The appearance of normal numbers of antibody-forming cells, and the restoration of antibody titres at week 4 correlated with the return of newly formed B cells in a normal marginal zone. An unexpected observation was that marginal zone macrophages did not return until 10 weeks after transplantation, thereby making the necessity for these cells in the normal TI-2 response unlikely. We conclude that normal anti-TI-2 responses (onset and peak titres) can be restored by autotransplantation of splenic tissue. B cells and marginal zone organization are responsible for this response, for which marginal zone macrophages seem expendable. The partial protection against overwhelming post-splenectomy infections, given by autotransplants, can thus be explained by restorative capabilities of these implants on antigen presentation and antibody formation against TI-2 antigens, and not by an increase (compared with splenectomized individuals) of phagocytosis by marginal zone macrophages.     

Marginal zone and mantle cell lymphomas: assessment of cytomorphology in subtyping small B-cell lymphomas

The diagnosis of malignant lymphomas by fine-needle aspiration biopsy (FNAB) is increasing in utilization. The cytomorphologic distinction among the small B-cell lymphomas may be quite difficult. We are unaware of anyone who has compared directly mantle cell lymphoma (MCL) and marginal zone lymphoma (MZL) in FNAB. Our major goal was to examine the cytomorphologic attributes of MCL and MZL and to look for features distinctive of or suggestive of either neoplasm. Seven immunophenotypic MCL and seven immunophenotypic MZL aspirates were evaluated for a number of cytomorphologic features in direct smears. Features favoring MCL include a relatively monomorphic cellular population, prominent nuclear membrane contour irregularities, and mitotic figures. Conversely, a polymorphic cellular population suggested MZL. However, due to extensive overlap of specific cytologic features, the two lymphomas cannot be definitively distinguished based solely on cytomorphology. Although there are cytomorphologic attributes suggestive of either MCL or MZL, considerable overlap exists. Based on an individual case basis, the distinction cannot be made reliably by morphology alone; ancillary studies, e.g., immunophenotyping, are essential.     

Ion channels and their functional role in vascular endothelium

Endothelial cells (EC) form a unique signal-transducing surface in the vascular system. The abundance of ion channels in the plasma membrane of these nonexcitable cells has raised questions about their functional role. This review presents evidence for the involvement of ion channels in endothelial cell functions controlled by intracellular Ca(2+) signals, such as the production and release of many vasoactive factors, e.g., nitric oxide and PGI(2). In addition, ion channels may be involved in the regulation of the traffic of macromolecules by endocytosis, transcytosis, the biosynthetic-secretory pathway, and exocytosis, e.g., tissue factor pathway inhibitor, von Willebrand factor, and tissue plasminogen activator. Ion channels are also involved in controlling intercellular permeability, EC proliferation, and angiogenesis. These functions are supported or triggered via ion channels, which either provide Ca(2+)-entry pathways or stabilize the driving force for Ca(2+) influx through these pathways. These Ca(2+)-entry pathways comprise agonist-activated nonselective Ca(2+)-permeable cation channels, cyclic nucleotide-activated nonselective cation channels, and store-operated Ca(2+) channels or capacitative Ca(2+) entry. At least some of these channels appear to be expressed by genes of the trp family. The driving force for Ca(2+) entry is mainly controlled by large-conductance Ca(2+)-dependent BK(Ca) channels (slo), inwardly rectifying K(+) channels (Kir2.1), and at least two types of Cl( -) channels, i.e., the Ca(2+)-activated Cl(-) channel and the housekeeping, volume-regulated anion channel (VRAC). In addition to their essential function in Ca(2+) signaling, VRAC channels are multifunctional, operate as a transport pathway for amino acids and organic osmolytes, and are possibly involved in endothelial cell proliferation and angiogenesis. Finally, we have also highlighted the role of ion channels as mechanosensors in EC. Plasmalemmal ion channels may signal rapid changes in hemodynamic forces, such as shear stress and biaxial tensile stress, but also changes in cell shape and cell volume to the cytoskeleton and the intracellular machinery for metabolite traffic and gene expression.     

Lymphocyte migration in the spleen: the effect of macrophage elimination.

To study the influence of macrophages on the migration and distribution of lymphocytes in the spleen, macrophages were eliminated from the spleen of mice by injection of liposomes in which DMDP was encapsulated. This leads to an elimination of macrophages in both the red pulp and marginal zone of the spleen within 1-2 days. In these animals the distribution of lymphocytes was determined by transfer of either syngeneic fluoresceinated or Ly 5 congeneic cells. It was found that after elimination of the macrophages the number of lymphocytes immigrating into the spleen had decreased, although a comparable mode of compartimentalization was found with an initial localization in the marginal zone and a subsequent distribution into the white pulp. After this elimination spleen macrophage subsets return with different kinetics, and in this way the influence of the red pulp macrophages, the marginal zone macrophages and the marginal metallophilic macrophages on lymphocyte immigration and redistribution could be investigated. A quantitative decrease of immigration was still found when red pulp and marginal metallophilic macrophages had repopulated their compartments, but was only fully restored when the last population to repopulate the spleen after treatment with DMDP-liposomes, the marginal zone macrophages, had returned. Experiments with isolated T and B cells showed that the elimination of macrophages had a profound effect on the localization of B cells in the white pulp, whereas it hardly affected T cells.     

Haemodynamics and arterial wall metabolism: their possible combined role in atherogenesis

An integrated model for the genesis of atherosclerosis is proposed on the basis of the evidence reported in the literature from the fields of haemodynamics and arterial wall metabolism. The model is based on the hypothesis of 'localized nutrient shortage' in the arterial wall at critical regions of the vascular tree, such as branchings, bendings, stenosis etc. In particular, it is proposed that a tissue deficit of glucose and oxygen, more pronounced at those regions, may be the main cause of endothelial dysfunction and lesion initiation. LDL-cholesterol level and hypertension are included as strongly interacting risk factors, and new explanations are provided for the effects of smoking and diabetes. For the latter factors, transport limitations in the lumen and/or in the tissue are likely to interact with wall metabolism; in the case of smoking, additional competition of CO and O2 within the tissue is suggested, and for diabetes, the impaired uptake of glucose by the tissue is proposed as the main causal factor. Also, the incorporation of secondary risk factors to the model is shown to be feasible on the basis of their suggested action mechanism. It is concluded that the study of nutrients and LDL transport at regions of complex arterial geometry in connection with wall metabolic requirements can provide a better understanding of the atherogenic process.     

Genesis of a new spleen focus-forming virus: possible role of MCF viruses

A Friend mink cell focus-inducing (Fr-MCF) virus isolated from a Friend tumor cell line was able to induce acute erythroleukemia associated with polycythemia when injected as a Friend murine ecotropic leukemia virus (F-MuLV) pseudotype into adult Swiss and ICFW mice. One virus isolate recovered from leukemic cells and designated as FV-F3 presented the following properties: (i) persistence of the same leukemogenic power when propagated in vivo and in vitro; (ii) in vivo spleen focus-forming (SFFV) capacity; (iii) presence of erythropoietin (EPO)-independent CFU-E in leukemic animals; (iv) expression of a 32 RNA specifically recognized by a SFFV probe, in FV-F3 infected cells; and (v) expression in FV-F3-infected cell of polypeptides in the range of gp52 SFFV. Peptide analysis of these products revealed close similarities with the parental MCF virus. These data suggest that a SFFV genome arose by genetic recombinational events involving MCF virus.     

Marginal zone of the spleen and the development and localization of specific antibody-forming cells against thymus-dependent and thymus-independent type-2 antigens.

In order to study the precise localization pattern of anti-TNP antibody-forming cells (AFCs) during the early primary immune response against TNP conjugated TD (thymus-dependent) and TI-2 (thymus-independent type-2) antigens, rats received an intravenous injection with either TNP-keyhole limpet haemocyanin (KLH) or with TNP-Ficoll. Anti-TNP AFCs developed in the spleen already at 2 days after injection of the antigens as demonstrated with our immunoenzyme technique for the detection of specific AFCs. In order to obtain information on the relationship between the non-lymphoid cells in the marginal zone (MZ) and the localization of AFCs, simultaneous staining for marginal metallophils and MZ macrophages (MZM) was performed using the monoclonal antibody ED3. AFCs were not found in the marginal zone (MZ), but the bulk of the cells in the white pulp were found in the outer part of the periarteriolar lymphocyte sheaths (PALS) close to the border between PALS and MZ. The precise localization of the anti-TNP AFCs in the outer part of the PALS resembled the localization of marginal metallophils but the latter cells were mainly present in the outer part of the follicles. So, the present results did not indicate a close relationship between marginal zone macrophages or marginal metallophils and anti-TNP AFCs, neither in the immune response to TD antigens nor in that to T1-2 antigens.     

The possible relationship between the pineal gland and red cell destruction by the spleen

Summary After pinealectomy we were able to observe an accumulation of iron pigment in the histiocytes of the cords and of the follicles of the spleen in the rat, parallel with a slight increase in the enzymatic activity of the histiocytes and hypertrophy of the argentophil reticulum. The accumulation of iron and the enzymatic activity can be further increased by subcutaneous injection of trypan blue.The working hypothesis is proposed that pinealectomy leads directly to an increase in the histiocytic activity in general and in the red cell destruction by the spleen in particular.

---

Über eine mögliche Beziehung zwischen der Glandula pinealis und dem Abbau von Erythrocyten in der Milz

Zusammenfassung Nach Pinealektomie konnte eine Anhäufung von Eisenpigment in den Histiocyten der Pulpastränge und der Follikel in der Rattenmilz festgestellt werden; parallel damit ging eine leichte Erhöhung der enzymatischen Aktivität der Histiocyten und eine Hypertrophie des argyrophilen Reticulums. Die Anhäufung von Eisenpigment und Erhöhung der enzymatischen Aktivität kann weiter gesteigert werden durch subcutane Injektion von Trypan-Blau. Folgende Arbeitshypothese wird zur Erklärung dieser Tatsache vorgeschlagen: Die Pinealektomie führt unmittelbar zu einer Erhöhung der Aktivität der Histiocyten im allgemeinen und des Abbaues der roten Blutkörperchen durch die Milz im besonderen.

---

---

This work was supported by CNR (Grant Nr. 115/1111/1051/).     

The role of TRPM channels in cell death

Transient receptor potential (TRP) channels of the melastatin-like family (TRPM) play critical roles in mediating cellular responses to a wide range of physiological stimuli that, under certain situations, can induce cell death. To date, two TRPM family members, TRPM2 and TRPM7, have been implicated directly as central components of cell death pathways. TRPM2, a Ca²⁺-permeant, non-selective cation channel, senses and responds to oxidative stress levels in the cell. TRPM7 is required for cell viability and has been proposed recently to mediate stress-induced cell death in the central nervous system. We review here the evidence for the involvement of these TRPM channels in cell death processes and discuss the mechanisms by which TRPM channel activation occurs. The ability to attenuate expression levels and functionality of these channels is necessary to understand the involvement of TRPM in cell death and we evaluate current approaches for modulation of TRPM channel function. Finally, we discuss the possibility that TRPM channels may provide therapeutic targets for degenerative diseases involving oxidative stress-related pathologies including diabetes and Alzheimers disease.     

Lymphocyte traffic and lymphocyte destruction in murine malaria.

Normal lymphocytes labelled with 51Cr were injected into mice at various stages of lethal and non-lethal malaria infections. Marked alterations were seen in the uptake into spleen and liver, which correlated with the outcome of the infection. Non-lethal infections and lethal infections in mice protected by vaccination caused increased uptakes, especially in the liver. In lethal infections, particularly Plasmodium berghei, uptakes were below normal values at certain times: this was apparently due to destruction of lymphocytes, probably caused by autoantibody.     

Contractile potentials of vascular chambers outside the heart: Their possible role in helping to power the circulation

While the cell is the basic biological unit, the contractile chamber follows closely in fundamental importance. Understanding the heart, the circulation and other systems in the body requires one, first, to recognize that common factor and basic unit, the contractile chamber. The heart is just one of many organs composed of contractile chambers. Some individuals do survive, despite a period when their hearts appeared to be doing little or nothing. Cases are cited which illustrate this seeming discrepancy between cardiac delinquency and patient's longevity. Some extra-cardiac propulsive mechanism must be identified to explain such cases. The extrapericardial vessels contain muscles which must have a dynamic role in the circulation of blood, supplementing, complementing, and perhaps even replacing cardiac action. In addition to transplants, and artificial hearts, the possibilities of enhancing the role of the extra-cardiac circulatory mechanisms (already provided by nature) should be studied.     

Possible role of mast cell membrane structures in the enhancement of spleen cell proliferation

The role of mast cells and their mediators in the regulation of immune processes is an area of current interest. In previous studies, we demonstrated that rat peritoneal mast cells and their supernatants enhance the spontaneous and mitogen-induced proliferation of immunocytes. The results of this paper indicate that the enhancing factor in mast cell supernatants is not dependent on mast cell activation or on the release of mediators from within the mast cell. Instead it seems to be due to the passive diffusion of surface structures during mast cell culture. Pretreatment of mast cells with glutaraldehyde did not alter the ability of intact mast cells to enhance spleen cell proliferation. In contrast, mast cells lost their enhancing ability if they were pretreated with trypsin followed by glutaraldehyde fixation. Based on these data, we suggest that protein membrane structures on the mast cell surface are responsible for a contact cooperation between mast cells and spleen cells and that they cause the enhancing effect on spleen cell proliferation. This type of interaction may be responsible for the regulation of immune cell function during local immune reactions.