Studies on the liver sequestration of lymphocytes bearing membrane-associated galactose-terminal glycoconjugates: reversal with agents that effectively compete for the asialoglycoprotein receptor

Interactions with Asialo-Glycoprotein Receptors and Platelets Are Dispensable for CD8+ T Cell Localization in the Murine Liver

Liver-resident CD8⁺ T cells can play critical roles in the control of pathogens, including Plasmodium and hepatitis B virus. Paradoxically, it has also been proposed that the liver may act as the main place for the elimination of CD8⁺ T cells at the resolution of immune responses. We hypothesized that different adhesion processes may drive residence versus elimination of T cells in the liver. Specifically, we investigated whether the expression of asialo-glycoproteins (ASGPs) drives the localization and elimination of effector CD8⁺ T cells in the liver, while interactions with platelets facilitate liver residence and protective function. Using murine CD8⁺ T cells activated in vitro, or in vivo by immunization with Plasmodium berghei sporozoites, we found that, unexpectedly, inhibition of ASGP receptors did not inhibit the accumulation of effector cells in the liver, but instead prevented these cells from accumulating in the spleen. In addition, enforced expression of ASGP on effector CD8⁺ T cells using St3GalI-deficient cells lead to their loss from the spleen. We also found, using different mouse models of thrombocytopenia, that severe reduction in platelet concentration in circulation did not strongly influence the residence and protective function of CD8⁺ T cells in the liver. These data suggest that platelets play a marginal role in CD8⁺ T cell function in the liver. Furthermore, ASGP-expressing effector CD8⁺ T cells accumulate in the spleen, not the liver, prior to their destruction.

Diverse Virus and Host-Dependent Mechanisms Influence the Systemic and Intrahepatic Immune Responses in the Woodchuck Model of Hepatitis B

Woodchuck infected with woodchuck hepatitis virus (WHV) represents the pathogenically nearest model of hepatitis B and associated hepatocellular carcinoma (HCC). This naturally occurring animal model also is highly valuable for development and preclinical evaluation of new anti-HBV agents and immunotherapies against chronic hepatitis (CH) B and HCC. Studies in this system uncovered a number of molecular and immunological processes which contribute or likely contribute to the immunopathogenesis of liver disease and modulation of the systemic and intrahepatic innate and adaptive immune responses during hepadnaviral infection. Among them, inhibition of presentation of the class I major histocompatibility complex on chronically infected hepatocytes and a role of WHV envelope proteins in this process, as well as augmented hepatocyte cytotoxicity mediated by constitutively expressed components of CD95 (Fas) ligand- and perforin-dependent pathways, capable of eliminating cells brought to contact with hepatocyte surface, including activated T lymphocytes, were uncovered. Other findings pointed to a role of autoimmune response against hepatocyte asialoglycoprotein receptor in augmenting severity of liver damage in hepadnaviral CH. It was also documented that WHV in the first few hours activates intrahepatic innate immunity that transiently decreases hepatic virus load. However, this activation is not translated in a timely manner to induction of virus-specific T cell response which appears to be hindered by defective activation of antigen presenting cells and presentation of viral epitopes to T cells. The early WHV infection also induces generalized polyclonal activation of T cells that precedes emergence of virus-specific T lymphocyte reactivity. The combination of these mechanisms hinder recognition of virus allowing its dissemination in the initial, asymptomatic stages of infection before adaptive cellular response became apparent. This review will highlight a range of diverse mechanisms uncovered in the woodchuck model which affect effectiveness of the anti-viral systemic and intrahepatic immune responses, and modify liver disease outcomes. Further exploration of these and other mechanisms, either already discovered or yet unknown, and their interactions should bring more comprehensive understanding of HBV pathogenesis and help to identify novel targets for therapeutic and preventive interventions. The woodchuck model is uniquely positioned to further contribute to these advances.

The three Rs: Recruitment, Retention and Residence of leukocytes in the liver

The composition of leukocytes in the liver is highly distinct from that of the blood and lymphoid organs. In particular, the liver is highly enriched in non-conventional T cells such as natural killer T (NKT) cells, γδ T cells and mucosal-associated invariant T cells. In addition, there are significant populations of tissue-resident NK cells (or innate lymphoid cells (ILC1)) and memory CD8+ T cells. These cells are joined in conditions of inflammation by neutrophils, monocytes and macrophages. In recent years a multitude of studies have generated insights into how these cells arrest, move and remain resident in the liver. This new understanding has largely been due to the use of intra-vital microscopy to track immune cells in the liver, coupled with gene expression profiling and parabiosis techniques. These studies have revealed that leukocyte recruitment in the liver does not correspond to the classical paradigm of the leukocyte adhesion cascade. Rather, both lymphoid and myeloid cells have been found to adhere in the liver sinusoids in a platelet-dependent manner. Leukocytes have also been observed to patrol the hepatic sinusoids using a characteristic crawling motility. Moreover, T cells have been observed surveying hepatocytes for antigen through the unique fenestrated endothelium of the liver sinusoids, potentially negating the need for extravasation. In this review we highlight some of these recent discoveries and examine the different molecular interactions required for the recruitment, retention and-in some cases-residence of diverse leukocyte populations within the liver.

Reversible off and on switching of prion infectivity via removing and reinstalling prion sialylation

The innate immune system provides the first line of defense against pathogens. To recognize pathogens, this system detects a number of molecular features that discriminate pathogens from host cells, including terminal sialylation of cell surface glycans. Mammalian cell surfaces, but generally not microbial cell surfaces, have sialylated glycans. Prions or PrP^Sc are proteinaceous pathogens that lack coding nucleic acids but do possess sialylated glycans. We proposed that sialylation of PrP^Sc is essential for evading innate immunity and infecting a host. In this study, the sialylation status of PrP^Sc was reduced by replicating PrP^Sc in serial Protein Misfolding Cyclic Amplification using sialidase-treated PrP^C substrate and then restored to original levels by replication using non-treated substrate. Upon intracerebral administration, all animals that received PrP^Sc with original or restored sialylation levels were infected, whereas none of the animals that received PrP^Sc with reduced sialylation were infected. Moreover, brains and spleens of animals from the latter group were completely cleared of prions. The current work established that the ability of prions to infect the host via intracerebral administration depends on PrP^Sc sialylation status. Remarkably, PrP^Sc infectivity could be switched off and on in a reversible manner by first removing and then restoring PrP^Sc sialylation.

Hepatocyte-mediated cytotoxicity and host defense mechanisms in the alcohol-injured liver

The consumption of alcohol is associated with many health issues including alcoholic liver disease (ALD). The natural history of ALD involves the development of steatosis, inflammation (steatohepatitis), fibrosis and cirrhosis. During the stage of steatohepatitis, the combination of inflammation and cellular damage can progress to a severe condition termed alcoholic hepatitis (AH). Unfortunately, the pathogenesis of AH remains uncharacterized. Some modulations have been identified in host defense and liver immunity mechanisms during AH that highlight the role of intrahepatic lymphocyte accumulation and associated inflammatory cytokine responses. Also, it is hypothesized that alcohol-induced injury to liver cells may significantly contribute to the aberrant lymphocytic distribution that is seen in AH. In particular, the regulation of lymphocytes by hepatocytes may be disrupted in the alcoholic liver resulting in altered immunologic homeostasis and perpetuation of disease. In recent studies, it was demonstrated that the direct killing of activated T lymphocytes by hepatocytes is facilitated by the asialoglycoprotein receptor (ASGPR). The ASGPR is a well-characterized glycoprotein receptor that is exclusively expressed by hepatocytes. This hepatic receptor is known for its role in the clearance of desialylated glycoproteins or cells, yet neither its physiological function nor its role in disease states has been determined. Interestingly, alcohol markedly impairs ASGPR function; however, the effect alcohol has on ASGPR-mediated cytotoxicity of lymphocytes remains to be elucidated. This review discusses the contribution of hepatocytes in immunological regulation and, importantly, how pathological effects of ethanol disrupt hepatocellular-mediated defense mechanisms.

Hepatocyte cytotoxicity is facilitated by asialoglycoprotein receptor

It has been recently identified that hepatocytes can act as cytotoxic effectors and can kill contacted cells by way of CD95 ligand-CD95 and perforin-dependent pathways. However, it remained unknown whether hepatocyte-mediated cell killing is indiscriminant or is directed toward targets with particular cell surface characteristics, as well as whether hepatocytes have the capacity to directly eliminate contacted lymphocytes. In this study, we found that desialylation of surface glycoproteins significantly augments cell susceptibility to hepatocyte-mediated killing. Using asialofetuin as a competitive ligand, and by silencing gene transcription with specific small interfering RNA, we found that the asialoglycoprotein receptor (ASGPR) is involved in hepatocyte recognition of cells predestined for killing, including activated autologous T lymphocytes.

CONCLUSION

Hepatocytes are constitutively equipped in the molecular machinery capable of eliminating cells brought into contact with their surface in a manner that is reliant, at least in part, upon the recognition of terminally desialylated glycoproteins by hepatocyte ASGPR. The study adds a new dimension to the physiological role of hepatic ASGPR and provides further evidence that hepatocytes can actively contribute to intrahepatic immune regulation and moderation of the local inflammatory response.

Hepadnaviral infection augments hepatocyte cytotoxicity mediated by both CD95 ligand and perforin pathways

BACKGROUND/AIM

Recently, we documented that hepatocytes can eliminate contacted cells via the CD95 ligand (CD95L)-CD95 pathway and that they are also equipped in perforin and granzyme B and can eradicate other cells via the granule exocytosis mechanism. The aim of this study was to assess whether hepadnaviral infection modifies hepatocyte-mediated cell killing.

METHODS

Primary hepatocytes from woodchucks with progressing or resolved hepadnaviral hepatitis and hepatocyte lines transfected with woodchuck hepatitis virus (WHV) genes were examined for cytotoxic effector activity against cell targets susceptible to CD95L and/or perforin-dependent killing. Hepatocytes from healthy animals served as controls.

RESULTS

Actively progressing and resolved hepadnaviral hepatitis is associated with a significantly greater capacity of hepatocytes to kill contacted cells. Both hepatocyte CD95L- and perforin-dependent cytotoxicity were augmented. Hepatocytes transfected with WHV X gene, but not those with complete WHV genome or virus envelope or core gene, transcribed significantly more CD95L and perforin and killed cell targets more efficiently. Exposure to interferon-gamma profoundly enhanced hepatocyte cell killing.

CONCLUSIONS

Hepatocyte cytotoxic potential is significantly augmented during and following resolution of active hepadnaviral hepatitis. Hepatocyte cytotoxic activity may contribute to both liver physiological functions and the pathogenesis and progression of liver disease, including viral hepatitis.

Hepatocytes can induce death of contacted cells via perforin-dependent mechanism

The liver displays unique immunological properties including the ability to remove aberrant cells and pathogens and to induce peripheral immunotolerance. We have previously demonstrated that hepatocytes can cause cell death by a CD95 ligand-mediated mechanism. Here, we provide evidence that hepatocytes can kill other cells via a perforin-dependent pathway. Using cultured woodchuck hepatocytes and human liver cells as well as freshly isolated woodchuck, mouse, and human hepatocytes, we show that hepatocyte-mediated death of CD95-deficient target cells requires microtubule polymerization, a feature of the granule exocytosis-mediated cytotoxicity. Neutralizing anti-perforin antibodies and short-hairpin RNA directed against perforin messenger RNA confirmed the involvement of perforin in hepatocyte-mediated cell killing.

CONCLUSION

This study shows that hepatocytes express biologically competent perforin capable of killing susceptible cells and emphasizes the role of hepatocytes as cytotoxic effectors. This also is the first demonstration of perforin in a non-lymphoid cell type.

The composition of intrahepatic lymphocytes: shaped by selective recruitment?

Intrahepatic lymphocytes have a distinct subset composition and phenotype. Compared with lymphoid tissues, the frequency of natural killer (NK) cells, NKT cells and gammadelta T cells among total lymphocytes is increased within the liver, and alphabeta T cells are predominantly effector/memory cells. Divergent hypotheses on the origin of intrahepatic T cells have emerged to explain this; in these hypotheses, either local development or selective recruitment of cells into the liver dominates. This Opinion highlights findings showing that the migratory preferences of lymphocyte subsets reflect their representation within the liver surprisingly well, suggesting that the composition of intrahepatic lymphocytes, in the absence of inflammation, is largely shaped by the dynamics of cell entry and exit into and from the liver.

Monitoring biodistribution of glycoproteins with modified sugar chains

Natural human interferon (hIFN)-gamma has mainly biantennary complex-type sugar chains. Previously, we successfully remodeled its sugar chain structure into: (a) highly branched types; or (b) highly sialylated types, by overexpression of: (a) N-acetylglucosaminyltransferase (GnT)-IV and/or GnT-V; or (b) sialyltransferases, in Chinese hamster ovary (CHO) cells. In addition, we prepared asialo hIFN-gammas by treatment with sialidase in vitro. In the present study, we assessed the bioactivity of remodeled hIFN-gamma in terms of antiviral activity, anticellular activity, and biodistribution. Structural changes to the sugar chains did not have a significant influence on the antiviral and anticellular activities of hIFN-gamma, although the attachment of the sugar chain itself affected both activities. However, the biodistribution differed significantly; the number of exposed galactose residues was the major determinant of the specific distribution to the liver and blood clearance rate of hIFN-gamma. This phenomenon was considered to be mediated by the hepatic asialoglycoprotein receptor (ASGP-R), and we showed a linear, not exponential, enhancement of the distribution to the liver with an increase in the number of exposed galactose residues. We also confirmed this tendency using fibroblast growth factor (FGF). Our observation is not the same as the "glycoside cluster effect." We thus provide important information on the character of modified recombinant glycoproteins.

Glycosylinositol Phospholipid Anchors of the Scrapie and Cellular Prion Proteins Contain Sialic Acid

The only identified component of the scrapie prion is PrPSc, a glycosylinositol phospholipid (GPI)-linked protein that is derived from the cellular isoform (PrPC) by an as yet unknown posttranslational event. Analysis of the PrPSc GPI has revealed six different glycoforms, three of which are unprecedented. Two of the glycoforms contain N-acetylneuraminic acid, which has not been previously reported as a component of any GPI. The largest form of the GPI is proposed to have a glycan core consisting of Man alpha-Man alpha-Man-(NeuAc-Gal-GalNAc-)Man-GlcN-Ino. Identical PrPSc GPI structures were found for two distinct isolates or "strains" of prions which specify different incubation times, neuropathology, and PrPSc distribution in brains of Syrian hamsters. Limited analysis of the PrPC GPI reveals that it also has sialylated glycoforms, arguing that the presence of this monosaccharide does not distinguish PrPC from PrPSc.

Compartmentalization of the peripheral immune system

The periphery of the immune system--as opposed to the central lymphoid organs--contains inhomogeneously distributed B and T cells whose phenotype, repertoire, developmental origin, and function are highly divergent. Nonconventional lymphocytes bearing a phenotype that is rare in the blood, spleen, or lymph nodes of undiseased individuals are encountered at high frequency in different localizations, e.g., alpha/beta TCR+CD4-CD8- cells in the bone marrow and gut epithelium, particular invariant gamma/delta TCR+CD4-CD8 alpha+CD8 beta- and gamma/delta TCR+CD4-CD8 alpha-CD8 beta- T cells in various epithelia, or CD5+ B cells in the peritoneum. The antigen receptor repertoire is different in each localization. Thus, different gamma/delta TCR gene products dominant in each site, and the proportion of cells expressing transgenic and endogenous alpha/beta TCR and immunoglobulin gene products follows a gradient, with a maximum of endogenous gene expression in the peritoneum, intermediate values in other peripheral lymphoid organs (spleen, lymph nodes), and minimum values in thymus and bone marrow. Forbidden T cells that bear self-superantigen-reactive V beta gene products are physiologically detected among alpha/beta TCR+CD4-CD8- lymphocytes of the bone marrow, as well as in the gut. Violating previous ideas on self-tolerance preservation, self-peptide-specific gamma/delta T cells are present among intestinal intraepithelial lymphocytes, and CD5+ B cells produce low-affinity crossreactive autoantibodies in a physiological fashion. It appears that, in contrast to the bulk of T and B lymphocytes, certain gamma/delta and alpha/beta T cells found in the periphery, as well as most CD5+ B cells, do not depend on the thymus or bone marrow for their development, respectively, but arise from different, nonconventional lineages. In addition to divergent lineages that are targeted to different organs guided by a spatiotemporal sequence of tissue-specific homing receptors, local induction or selection processes may be important in the diversification of peripheral lymphocyte compartments. Selection may be exerted by local antigens, antigen-presenting cells whose function varies in each anatomical localization, cytokines, and cell-matrix interactions, thus leading to the expansion and maintenance of some clones, whereas others are diluted out or deleted. The spatial compartmentalization of lymphocytes in different microenvironments has major functional consequences and leads to a partial fragmentation of immunoregulatory circuits at the local level. Lymphocytes residing in certain antigen-exposed compartments are likely to combat tissue-specific pathogens or self-proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of supravital fluorochromes used to analyze the in vivo homing of murine lymphocytes on cellular function

A number of supravital fluorochromes are available to study lymphocyte homing in vivo. These include fluorescein isothiocyanate (FITC), which binds to cell surface proteins; Hoechst 33342, which binds to AT rich regions of cellular DNA; and the lipid bilayer incorporated dyes PKH-2 and PKH-26. The relative advantages and disadvantages of each of these probes for analyzing murine lymphocyte homing are as yet poorly understood. We evaluated the effects of each dye on labeling efficiency, as well as cell viability, homing, mitogen responsiveness and cytotoxicity. PKH-26 provided long-term labeling (up to 15 days) with the least detrimental effects on cellular function. Detection of FITC in vivo was impaired by tissue autofluorescence, and the dye acted as a co-mitogen for lectin or IL-2-induced proliferation. Hoechst 33342 eluted from cells over a few hours and inhibited lymphocyte proliferation. PKH-2 had detrimental effects on cell viability and resulted in the down-modulation of peripheral lymph node homing receptor expression. None of the probes interfered with the induction of cytotoxic lymphocytes by IL-2. While these fluorochromes are easy to use and provide powerful tools to analyze the lymphocyte localization in vivo, our experiments demonstrate that important limitations are imposed by each probe that need to be considered by investigators during the design and interpretation of experiments.

Interleukin-2 stimulated T cell receptor V gamma 3 positive thymocytes do not migrate to the skin

T cell receptor (TcR) V gamma 3+ thymocytes, which only develop in the fetal thymus, migrate to the skin. IL-2 stimulation of fetal day 18 murine thymocytes results in a cell population of which 45% of the cells express the TcR V gamma 3. In this study, we describe that those IL-2 cultured TcR V gamma 3+ thymocytes have the killing capacity of lymphokine activated killer cells: NK-susceptible as well as NK-resistant tumor cell lines were killed in an MHC-unrestricted manner. Because of these findings, IL-2-expanded TcR V gamma 3+ thymocytes could have a potential use in adoptive immunotherapy for skin-located tumors. Therefore, we analyzed the migration pattern of IL-2-cultured TcR V gamma 3+ thymocytes upon i.v. injection. We describe their initial entrapment in the lungs and subsequent accumulation in the liver. Localization in the skin was practically absent, and did not differ from that of IL-2 cultured adult thymocytes (mainly TcR alpha beta +). The migration pattern was identical in adult and newborn normal mice, and in adult nude mice. Analysis of the expression of asialo-GM1 revealed that it increased strongly after IL-2 culture. The relevance of this change in asialo-GM1 expression with reference to the migration upon i.v. injection is discussed. This study indicates that an improved understanding of the determinants of in vivo localization of IL-2 cultured cells may lead to improved strategies for adoptive immunotherapy of cancer.

Mechanisms of pertussis toxin inhibition of lymphocyte-HEV interactions. I. Analysis of lymphocyte homing receptor-mediated binding mechanisms

The molecular mechanisms by which pertussis toxin (PTX) inhibits lymphocyte homing to peripheral lymph nodes (PLN) remain poorly understood. PTX-treated lymphocytes express homing receptors, yet cannot extravasate into PLN in vivo. Methylation of PTX, a procedure known to inactivate the B-oligomer of the toxin, restored high endothelial venule (HEV) binding capacity. In vitro studies established that toxin exposure inhibited the accessory role of LFA-1 in HEV binding. In contrast, PTX-exposed lymphocytes exhibited normal MEL-14-mediated HEV binding. Analysis of membrane fluidity revealed a 20% decrease in fluorescence polarization in PTX-exposed lymphocytes. On the basis of the current experiments, we propose a "zipper" model of lymphocyte-HEV interaction, in which lateral mobility of adhesion receptors in the cell membrane toward a site of endothelial contact is necessary to maintain adhesion against the shear force due to blood flow. PTX inhibits these processes by decreasing membrane fluidity, and by altering accessory adhesion molecule function.

Expression of Thomsen-Friedenreich (TF) antigens on lymphocytes. I. Distribution of cryptic and exposed TF antigens on murine lymphocytes from different lymphoid organs: detection with an anti-TF monoclonal antibody and peanut agglutinin

Cryptic Thomsen-Friedenreich (TF) antigens were detected by the lectin peanut agglutinin (PNA) on the surface of murine lymphocytes after treatment of cells with neuraminidase. Thereby, a particular TF antigen could be distinguished using a monoclonal anti-TF antibody 49H8. In contrast to the known general galactoside specificity of PNA, the mAb was restricted to Gal beta(1-3)GalNAc/GlcNAc. Preincubation of cells with PNA abolished mAb 49H8 binding completely. However, only the intensity of staining with PNA was reduced by prior incubation of cells with the mAb. Cryptic TF antigens detected by the mAb were expressed on 39% of murine bone marrow cells, 88% of thymocytes, 62% of lymph node cells, and 65% of spleen cells. On the other hand, over 80% of the lymphatic cells carried cryptic PNA binding sites independent of the lymphoid organ they derived. In the thymus, a subpopulation of cells (76%) could be detected by PNA without neuraminidase treatment. Twenty-eight percent of thymocytes carried exposed mAb binding sites, too. All of them were shown to express further binding sites for PNA constantly. Therefore, a subpopulation of PNA-reactive, immature thymocytes can be distinguished by the mAb 49H8. During activation of splenic lymphocytes with PHA, the lymphoblasts completely lost their cryptic mAb binding sites while PNA reactivity was not affected. We conclude that the anti-TF mAb recognizes a particular TF antigen exposed on thymocytes and present in a cryptic form on other lymphocytes. The number of cells carrying mAb 49H8 binding sites varied, dependent on the organ from which the lymphocytes derived. PNA-reactive lymphocytes are distributed homogeneously in the lymphoid organs.

Expression of Thomsen-Friedenreich (TF) antigens on lymphocytes. II. Loss of cryptic TF antigens during mitogenic activation of human T and B lymphocytes

Human peripheral blood lymphocytes (HPBL) were examined for the presence of cryptic Thomsen-Friedenreich (TF) antigens as detected by PNA or an anti-TF mAb (49H8) after neuraminidase treatment of the cell surface. Neither PNA nor the mAb bound to the cells before treatment with neuraminidase. After removal of surface sialic acid, all lymphocytes were PNA-reactive, and 85% of HPBL reacted with the mAb 49H8. Seventy-seven percent of nylon wool (NW)-eluted T cells (96% Leu 1+), 80% of enriched helper T cells (83% Leu 3a+), and 78% of suppressor/cytotoxic T cells (63% Leu 2a+) carried the cryptic TF determinant recognized by the mAb 49H8. Ninety-one percent of NW-adherent cells (68% Leu 10+, 5% Leu 1+) were also TF positive. In contrast to NW-eluted T cells which showed low to moderate mAb 49H8 binding, 48% of NW-adherent cells revealed strong binding of anti-TF mAb. With progressive activation of T cells by PHA, binding of mAb to the cryptic TF antigen completely disappeared on blast cells. The presence of TF antigens on small cells in the culture was only poorly affected. The same was observed for activation of B cells with PWM. On the other hand, binding sites for PNA did not change during blastogenesis. The disappearance of the particular, mAb 49H8-reactive TF antigen on T blast cells is not due to the loss of antigen in a distinct T cell subset, but occurs to an equal extent in the helper and suppressor/cytotoxic T cell subpopulations. Thus, the majority of peripheral T and B lymphocytes carries cryptic TF antigens. Activated T or B cell blasts, on the other hand, are deficient for the particular TF antigen detected by the mAb 49H8. We interpret these data as a modulation of certain TF antigens on effector cells in the course of lymphocyte activation.

In vivo localization of lymphocytes labelled with low concentrations of Hoechst 33342

Hoechst 33342 (HO 33342) is a fluorescent dye which binds specifically to DNA and can be used to label lymphocytes for in vivo migration studies. Lymphocytes were treated with varying concentrations of HO 33342 and assayed in vitro for effects on viability, mitogen-stimulated proliferation, and motility. In vivo traffic studies were performed to determine a dye concentration with minimal toxicity for lymphocytes, but sufficient fluorescence for detection of cells in frozen sections. The concentration reported to yield quantitative staining of nuclear DNA (10.7 microM, or 6 micrograms/ml) reduced motility and proliferative response, and resulted in an altered lymphocyte migration pattern compared to untreated lymphocytes. A concentration of 0.25 microM, however, produced no toxicity in the in vitro assays, and an in vivo migration pattern similar to that of untreated cells; lymphocytes stained with 0.25 microM HO 33342 for 30 min were readily observable in histological sections. This study indicates that the concentration of HO 33342 optimal for DNA staining may exert deleterious effects on in vivo lymphocyte traffic studies, and that far lower dye concentrations are more suitable for such studies.

Enhancement of human B-cell proliferation by a monoclonal antibody to CD43

Monoclonal antibodies (MoAb) to human leucocyte sialoglycoprotein, CD43, have been shown to deliver mitogenic signals to human T cells or to enhance T-cell proliferation induced by concanavalin A, anti-CD3 antibodies or phorbol ester. In this paper, we studied the effects of anti-CD43 MoAb B1B6 on the activation of human B cells. Anti-CD43 MoAb B1B6 was not mitogenic by itself for human B cells. However, when added together with TPA, both resting and in vivo activated tonsillar B cells, containing 5-10% and about 35% CD43+ respectively, responded with three- to fivefold higher proliferation compared to that obtained with TPA alone. A peak in the proliferative response was reached on day 3. Optimal proliferation was obtained when the antibody was present from the start of culturing. Addition of MoAb B1B6 together with a calcium ionophore, ionomycin, did not induce B-cell proliferation. Neither did mAb B1B6 sustain the growth of B cells that were already in the cell cycle, i.e. precultured with phorbol ester (PDB) and ionomycin for 3 days. The results are similar to those obtained with antibodies to CD22 and CD23 and show that early progression signals are delivered to resting B cells through CD43 in the presence of primary activators of protein kinase C.

Identification and characterization of a murine receptor for galactose-terminated glycoproteins

The asialoglycoprotein receptor, the hepatic binding lectin for galactose-terminated glycoproteins, has been isolated and characterized from human, rabbit and rat liver. Several recent studies have shown the existence of the same receptor in murine liver. However, the biochemical structure of the receptor in murine liver has not been resolved. In this paper, we describe the identification and purification of the receptor for asialoglycoproteins from murine liver. The purified receptor has three polypeptides with apparent molecular weights of 42,000, 45,000 and 51,000, respectively, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Furthermore, our studies suggest that the receptor from murine liver is very similar to its counterpart in rat liver, although some potential interesting differences have also been observed. Initial studies indicate that this receptor is well conserved in different mouse strains.

Positive effects of indomethacin on restoration of splenic nucleated cell populations in mice given sublethal irradiation

Splenic cellularity during the recovery phase after 400-R irradiation was evaluated in mice, in which the level of prostaglandin was regulated by indomethacin and exogenous prostaglandin E2, following sublethal irradiation. Two weeks after irradiation, administration to these mice of indomethacin, an inhibitor of prostaglandin synthesis, augmented the recovery of all nucleated spleen cell populations, whereas the thymus was drastically depopulated. This treatment had little effect upon the total number of bone marrow cells but inversed the ratio of PNA+/PNA- cells. Cell transfer experiments using heavily irradiated mice as recipients showed that the stem cell proliferation was positively affected by indomethacin treatment in the bone marrow rather than in the spleen. These results suggest that cell migration from primary lymphoid organs, particularly from the bone marrow to the spleen, is regulated by a prostaglandin-mediated system and that a prostaglandin E2 synthesis inhibition would have a positive effect on the restoration of peripheral nucleated cells following irradiation.

Alterations in lymphocyte recirculation within ultraviolet light-irradiated mice: efferent blockade of lymphocyte egress from peripheral lymph nodes

Ultraviolet irradiation (uvR) has been demonstrated to have profound effects on many functions of the immune system. In particular, exposure to this physical agent can alter the tissue distribution and function of a number of immunologically active cell types, even at sites remote from direct uvR exposure. The present investigation demonstrates that uvR exposure of mice induces an efferent blockade of lymphocyte egress from the peripheral lymph nodes which drain the irradiated skin, resulting in marked retention of lymphocytes. In vivo studies of this efferent blockade established that the condition appeared similar in mechanism to that induced by the administration of poly-inosinic:poly-citidylic acid, murine interferon alpha/beta and specific antigen. We were able to establish that a common mechanism in the genesis of an efferent lymphatic blockade may involve prostaglandin biosynthesis. The potential contribution of efferent blockade to the development of systemic suppression of contact hypersensitivity induced by uvR exposure is discussed.

Characterization of the in vitro interaction of PNAhi lymphocytes with the bone marrow and hepatic asialoglycoprotein receptors

We have previously identified an in vivo interaction between circulating PNAhi lymphoid cells and the hepatic asialoglycoprotein receptor, which results in a protracted liver sequestration of these cells. An in vitro frozen section binding assay was developed to study the interaction of PNAhi cells with the receptor in more detail. This assay confirmed that the sequestration of PNAhi lymphoid cells by the liver was mediated by the asialoglycoprotein receptor, as binding was inhibitable by coincubation with galactose, asialoglycoproteins, chelation of divalent cations, or a specific anti-asialoglycoprotein receptor antiserum. This frozen section binding assay was utilized to demonstrate the existence of a bone marrow asialoglycoprotein receptor which was found to be capable of binding to PNAhi lymphocytes or asialoglycoproteins bound to synthetic substrates. We further established that the bone marrow receptor differed both functionally and antigenically from its hepatic analogue.

Bone marrow engraftment efficiency is enhanced by competitive inhibition of the hepatic asialoglycoprotein receptor

The efficiency of pluripotent stem cell engraftment following bone marrow transplantation is predicated upon many poorly understood factors. These include the processes by which intravenously injected stem cells circulate and localize in microenvironments that contain the stromal elements necessary to facilitate their continued proliferation. We have recently established that lymphoid cells that bind the lectin peanut agglutinin are subject to prolonged sequestration following their interaction with the hepatic asialoglycoprotein receptor. Since bone marrow stem cells are also known to bind peanut agglutinin, we hypothesized that the physiologic function of the asialoglycoprotein receptor might significantly impair their ability to localize in anatomic sites where they are able to proliferate. Competitive inhibition with asialoglycoproteins was employed to establish a temporary receptor blockade during the initial 3-4 hr after transplantation. This procedure resulted in a 5- to 10-fold increase in splenic hematopoietic colony formation. Our findings suggest that inhibition of the liver asialoglycoprotein receptor during murine bone marrow transplantation results in more efficient stem cell localization to hematopoietic-inducing microenvironments. This enhancement in engraftment efficiency was paralleled by a more rapid recovery of peripheral blood leukocyte and platelet counts, an increase in megakaryocytic colony formation, as well as increased recipient survival. Techniques designed to inhibit the liver sequestration of bone marrow stem cells may have direct applicability to human bone marrow transplantation procedures.