Selective role for the p55 Kd TNF-alpha receptor in immune unresponsiveness induced by an acute viral encephalitis.

Brain infection by the laboratory strain challenge virus standard (CVS), a highly neurotropic strain of rabies virus, causes splenocytes to become less responsive to in vitro stimulation with ConA. CVS-induced immune unresponsiveness is less severe in mice lacking the p55 Kd TNF-alpha receptor (p55TNFR(-/-)) than in C57BL/6 mice, despite a similar invasion of the brain. Comparison of CVS infection in these two strains of mice indicated that decreased immune responsiveness is associated with: (1) an in vivo reduction of the percentages of Th1 (IL-2, IFN-gamma and TNF-alpha) but not of Th2 (IL-4) cytokine-secreting T cells; and (2) an in vivo increase of the percentages of CD25 and CD69-expressing splenocytes. In contrast, CVS-induced immune unresponsiveness is not associated with abnormal percentage of T, B, NK cells or monocytes in vivo. The reductions of the CD4/CD8 ratio and of splenocyte expression of I-A(b) during CVS infection are similar in p55TNFR(-/-) and C57BL/6 mice indicating that these two parameters are not linked to the decreased responsiveness of splenocytes. These data suggest that CVS-induced immune unresponsiveness is under the control of the p55 Kd TNF-alpha receptor. We propose that T cell activation through this receptor, in an environment of poor antigen presentation, results in a state of T cells characterized by the reduced production of IL-2, TNF-alpha and IFN-gamma in vivo, the decreased responsiveness of splenocytes to ConA stimulation in vitro and the expression of the activation markers CD25 and CD69.

Abortive rabies virus central nervous infection is controlled by T lymphocyte local recruitment and induction of apoptosis.

Nonfatal paralysis, induced by the attenuated Pasteur strain of rabies virus, is characterised by local and irreversible flaccid paralysis of the inoculated limbs. We characterised the spread and localisation of virus in the CNS of infected mice, determined the nature of cell injury and examined the role of the immune response. Data indicate that infection of BALB/c mice induced paralysis in 60% of infected mice, the others recovering without sequelae. In both groups of mice, virus was detected in restricted sub-populations of neurons from the brain and spinal cord, and intensity of the neuropathology correlated with levels of rabies RNA and apoptotic infected neurons. However, apoptosis of neurons and paralysis were not due to a direct deleterious effect of the virus, but induced by a T-dependent immune response, as evidenced by their absence in nude mice. Paralysed and asymptomatic mice developed a similar rabies virus-specific IgG2a antibody response, thus excluding the role of any modification of the humoral immune response. In contrast, three events were critically associated with the development of neurological symptoms: the amount of virus in the CNS, the level of apoptosis in both infected neurons and uninfected surrounding cells and the progressive parenchymal infiltration of CD4+ and CD8+ T cells at the site of infection. These data suggest that during nonfatal rabies infection, the levels of viral replication and primary degeneration of infected neurons by apoptosis could be responsible for the infiltration of T lymphocytes capable of inducing secondary degeneration of neural cells.

Urtica dioica agglutinin, a V beta 8.3-specific superantigen, prevents the development of the systemic lupus erythematosus-like pathology of MRL lpr/lpr mice.

The V beta 8.3-specific superantigenic lectin Urtica dioica agglutinin (UDA) was used to delete the V beta 8.3+ T cells in MRL lpr/lpr mice. In contrast to the systemic lupus erythematosus-like pathology which progresses with age in the phosphate-buffered saline-injected MRL lpr/lpr controls, UDA-treated animals did not develop overt clinical signs of lupus and nephritis. The pathogenic T cell clones thus reside within the V beta 8.3+ T cell population, which includes an expanded T cell clone described previously. Finally, UDA alters the production of autoantibodies in a sex-dependent manner.

The J beta segment of the T cell receptor contributes to the V beta-specific T cell expansion caused by staphylococcal enterotoxin B and Urtica dioica superantigens.

We have used a new polymerase chain reaction-based technique to analyze at the clonal level the CDR3 diversity and the J beta usage associated with the V beta-dependent T cell receptor (TCR) recognition of two superantigens: the staphylococcal enterotoxin B and the Urtica dioica agglutinin. Our results show that subset of J beta elements is preferentially expanded in a given V beta family, independently of the nature of the superantigen. By contrast, the CDR3 loop does not contribute significantly to the T cell expansion induced by the superantigens. We conclude that the J beta segment of the TCR beta chain, but not the CDR3 region, participates in superantigen binding, presumably by influencing the quaternary structure of the TCR beta chain.

Selective expansion followed by profound deletion of mature V beta 8.3+ T cells in vivo after exposure to the superantigenic lectin Urtica dioica agglutinin.

Urtica dioica agglutinin (UDA) is a superantigen that, in vitro, binds to specific carbohydrate structures on class II and induces a sixfold enrichment of V beta 8.3+ BALB/c mice splenic T cells. Superantigens have pleiotropic effects in vivo, causing the activation, proliferation, and deletion of specific T cells, but are heterogenous in regard to their effects on T cell tolerization. We, therefore, compared the responses of peripheral T cells from adult BALB/c mice with the i.v. injection of 50 micrograms UDA or the bacterial superantigen staphylococcal enterotoxin B (SEB) that also recognizes the V beta 8.3 gene product. The data presented indicate that activation, clonal expansion, anergy, and death of V beta 8.3+ T cells occur sequentially after UDA administration. Two days after UDA injection, the proportion of V beta 8.3+ T cells in the periphery is elevated to approximately twice that of normal mice. This expansion occurs in both CD4+ and CD8+ subsets. V beta 8.3+ T cells from UDA-primed mice are anergic to UDA restimulation and fail to proliferate or to produce IL-2. Futhermore, the proliferation of V beta 8.3+ T cells is followed by their rapid disappearance concomitant with their specific elimination by apoptosis. In 1 wk, all CD4+ V beta 8.3+ peripheral T cells are deleted. The decline of V beta 8.3+ T cells in the CD4+ subset is more than in the CD8+ subset. This occurs in thymectomized and in thymus-intact animals. Two months after UDA priming, the percentage of V beta 8.3+ T cells is still lower than in control mice.

Urtica dioica agglutinin. A superantigenic lectin from stinging nettle rhizome.

Urtica dioica agglutinin (UDA) is an unusual plant lectin that differs from all other known plant lectins with respect to its molecular structure and its extremely low specific agglutination activity. We recently reported that this small lectin (8.5 kDa) is a T cell mitogen distinguishable from classical T cell lectin mitogens by its ability to discriminate a particular population of CD4+ and CD8+ T cells as well as its capacity to induce an original pattern of T cell activation and cytokine production. The mechanism by which UDA activates T cells was investigated and compared with the conventional T cell mitogen Con A and the known superantigen staphylococcal enterotoxin B. Our data show that T cell proliferation induced by UDA is strictly dependent on AC expressing MHC class II molecules but is not MHC restricted. This proliferation can be partially inhibited by anti-I-A or anti-I-E mAb and completely blocked by a mAb recognizing monomorphic determinants on the Ia molecule. UDA indeed binds to specific carbohydrate structures present on class II molecules. UDA-induced T cell stimulation is dependent on TCR recognition of the unprocessed intact molecule in association with various Ia molecules. T cell response to UDA is clonally expressed and correlates with particular TCR V beta gene families usage. This stimulation leads to a sixfold enrichment of V beta 8.3+ T cells within 3 days. Therefore, UDA appears to use the same molecular mechanism as structurally unrelated bacterial or retroviral superantigens and we propose that this lectin is a superantigen. UDA, which is not a pathogenicity factor, could provide a useful probe for the analysis of T cell activation by superantigens.

B cells do not present antigen covalently linked to microspheres.

B cells have been shown to present antigen to T cells very efficiently through their capacity to capture antigens by their membrane immunoglobulin. This direct cognate interaction of T and B cells results in the proliferation and differentiation of B cells. This concept has been established using soluble proteins. However, most of the antigens to which the immune system is exposed are included in complex particulate structures such as bacteria or parasites. The capacity of B cells to present these large and complex antigens is still unclear. To address this question we have studied the presentation by trinitrophenyl (TNP)-specific B cells of the same antigen TNP-KLH (keyhole limpet haemocyanin), either in a soluble form or covalently linked to poly(acrolein) microspheres, from 0.25 to 1.5 microns in diameter. In the presence of irradiated splenocytes or purified macrophages as a source of antigen-presenting cells (APC), KLH-specific T cells proliferated in response to soluble TNP-KLH or to TNP-KLH coupled to beads. In contrast, TNP-specific memory B cells were totally ineffective in presenting the TNP-KLH beads to KLH-specific T cells whereas they presented very efficiently soluble TNP-KLH. Similar results were obtained with the A20 B lymphoma or with lipopolysaccharide (LPS)-activated TNP-specific B cells. These results therefore indicate that B cells are unable to present large size particulate antigens such as bacteria or parasites.

Mouse T-lymphocyte activation by Urtica dioica agglutinin. I.--Delineation of two lymphocyte subsets.

Urtica dioica agglutinin (UDA) is a mouse T-lymphocyte-specific mitogen endowed with proliferative characteristics different from ConA, the prototypic T-lymphocyte mitogen. In particular, UDA induces 2-3-fold-reduced thymidine incorporation as compared to ConA. In an attempt to define the basis of this reduced proliferation, we analysed whether UDA binds to a unique subset of T lymphocytes or whether it activates only a T-cell subset. Cytofluorimetric analysis showed that this lectin binds uniformly to all T lymphocytes and does not, on this criterion, distinguish a particular T-cell subset. We next analysed whether UDA provokes the activation of all T lymphocytes. This was carried out by measuring the increase in cell size and the induction of the p55 chain of the IL2 receptor. The analysis showed that, throughout the kinetics of cell activation, only one subset of T lymphocytes increased in size and expressed the p55 chain of the IL2 receptor, suggesting that UDA activates only a subpopulation of T cells. This conclusion was strengthened by the analysis of 5-bromo-2-deoxyuridine (BrdU) incorporation into the DNA of UDA-activated cells. Two populations were easily identifiable: a BrdU-negative subset consisting of all the small p55-negative lymphocytes, and a BrdU-labelled subset including all the large p55-positive cells. BrdU was incorporated in both CD4+ and CD8+ cells, indicating that UDA did not distinguish helper from cytotoxic T lymphocytes. In addition to the p55 chain of the IL2R, all cycling cells expressed the Pgp-1 activation marker. The T lymphocytes, which bound UDA but did not proliferate, remained fully susceptible to subsequent stimulation by ConA. In conclusion, the capacity to proliferate upon UDA binding differentiates a UDA-sensitive from a UDA-refractory subset among splenic mouse T lymphocytes.

Mouse T-lymphocyte activation by Urtica dioica agglutinin. II.--Original pattern of cell activation and cytokine production induced by UDA.

Urtica dioica agglutinin (UDA) is a T-lymphocyte-specific polyclonal activator that differs from ConA, the classical mouse T-cell mitogen, by inducing a late and limited proliferation of a distinct T-cell subset recruited among both CD4+ and CD8+ lymphocytes. We investigated the possibility that the particular kinetics may originate from UDA-specific activation processes in which the known early mandatory signals were completed only after an extended delay. We report that the time of contact required between lectin and the cell membrane to acquire the capacity to proceed into cell cycle was much longer (36-40 h) for UDA than for ConA (8-10 h). Addition of phorbol ester, which artificially induces PKC translocation, or ionomycin, which provokes Ca2+ mobilization, did not accelerate the proliferative kinetics, suggesting that these early mandatory signals are not the limiting factors in the delayed proliferation. The induction of c-myc was retarded in the UDA group, and there was a good correlation between the kinetics of c-myc induction and the kinetics of cell proliferation. The comparison of the level of transcription of the genes encoding different cytokines revealed additional differences between the two mitogens: the whole wave of cytokine gene expression was delayed with UDA. In particular, IL2, IL3 and IFN gamma gene expression was retarded compared to the ConA-induced single wave. An even later transcriptional wave took place at around 72 h for IL4 and IL5. Finally, this particular kinetics corresponded to an unusually high level of IL3 and IFN gamma and a low level of IL4 and IL5 gene transcripts.(ABSTRACT TRUNCATED AT 250 WORDS)

Clonal anergy of memory B cells in epitope-specific regulation.

Immunization of carrier (keyhole limpet hemocyanin (KLH)) primed mice with the hapten-carrier TNP-KLH induces specific suppression for the IgG anti-TNP-response without interfering with the response to epitopes on the carrier molecule. To examine the status of hapten-specific memory B cells from suppressed mice, highly enriched populations of TNP-specific memory B cells were purified from the spleen of TNP-KLH (control) or KLH/TNP-KLH (suppressed) immunized mice and tested in vitro for their ability to respond to TD or TI (TNP-KLH, TNP-LPS) antigenic challenge in presence of a KLH-specific Th cell line. Similar numbers of TNP-specific B cells with the characteristics of memory B cells were obtained from control and suppressed mice. TNP-specific B cells from suppressed mice could be triggered to IgG production by TNP-LPS but had an impaired ability to differentiate into IgG-secreting cells in response to TNP-KLH. This impaired IgG response to TNP-KLH was not due to an active suppression by a subset of TNP-specific B cells, or to an impedence of memory cells to a class switching but to an intrinsic memory B cell defect. TNP-specific B cells from suppressed mice were as efficient as memory B cells from control mice to present TNP-KLH to KLH-specific Th cells and to proliferate in response to T cell help. Our data support the view that the effector mechanism of epitope specific regulation does not interfere with the development of hapten-specific memory B cells but that these cells have an intrinsic defect that prevents their differentiation into active IgG antibody secreting cells in response to a T-dependent antigenic challenge.

Induction of murine hemopoietic growth factors by toxic shock syndrome toxin-1.

Toxic shock syndrome toxin-1 (TSST-1), an extra-cellular 22 kDa single chain protein produced by most Staphylococcus aureus strains isolated from patients with toxic shock syndrome (TSS), induces modifications of blood cell values similar to those observed during TSS. We therefore analyzed the effects of TSST-1 on the proliferation and differentiation of murine granulocyte-macrophage progenitor cells (CFU-culture) and the eventual role of endotoxin in this response. TSST-1 had no direct effect on the proliferation of CFU-culture and was unable to influence the CSF-induced proliferation and differentiation of these progenitors. In contrast, TSST-1 was a potent inducer in spleen cell cultures of a factor with an ability to induce both colony formation by bone marrow cells and proliferation of an IL-3-dependent cell line. Nanogram amounts of TSST-1 were able to induce the release of CSF activity in spleen cell cultures from both normal and LPS-hyporesponsive mice. Cells from C3H/HeJ mice were as responsive as cells from C3H/He Pas mice. Furthermore, in spleen cell cultures from normal mice, TSST-1 and LPS did not act synergistically to induce CSF activity. Nanogram amounts of TSST-1 were also able to induce CSF activity in vivo but failed to induce IL-3 activity in the serum and organ-conditioned media from TSST-1-treated mice.

Induction of colony-stimulating activity in mice by injection of liposomes containing lipophilic muramyl peptide derivatives.

Colony-stimulating factor (CSF) activity induction by lipophilic derivatives of three muramyl peptides, glyceryl dipalmitate-MDP derivatives, was studied in vivo and in vitro and compared to the activity of the same compounds incorporated within freeze-dried liposomes. Two lipophilic derivatives (MDP-GDP and MDPGBe-GDP) were able to induce CSF activity in vivo and in vitro. The incorporation of these compounds within appropriately designed liposomes composed of distearoylphosphatidylcholine and phosphatidylserine (DSPC/PS) increased their ability to induce CSF activity in vivo but completely abrogated their ability to induce CSF activity in vitro. Furthermore, the phospholipid composition of liposomes influenced the efficacy of glycopeptide liposomal incorporation. Thus, the serum CSF-inducing effect of MDP-GDP was considerably enhanced by incorporation of this compound within liposomes composed of DSPC/PS at a molar ratio 7:0.3 but was not modified if the DSPC/PS molar ratio was 7:3. The lipophilic derivative of MDP (D-D), MDP (D-D)-GDP, was unable to induce CSF activity in vivo or in vitro but surprisingly became active in vivo after entrapment within DSPC/PS liposomes (molar ratio 7:0.3). Our results show that appropriate liposomes may be suitable carriers to deliver CSF activity-inducing agents to macrophages in vivo.

Induction of colony-stimulating activity (CSA) by a synthetic muramyl peptide (MDP): synergism with LPS and activity in C3H/HeJ mice and in endotoxin-tolerized mice.

Injection of MDP into mice induces a rapid elevation of monocyte-macrophage CSA in the serum. This effect can also be observed in LPS-hyporesponsive C3H/HeJ mice. MDP and LPS induce CSA synergistically in normal mice. In contrast to the tolerance that is rapidly observed after repeated administration of LPS, MDP does not lose its capacity of inducing serum CSA after repeated injections. Repeated daily injections of MDP also fail to induce tolerance to the LPS-CSA inducing effect. Furthermore, whereas mice rendered tolerant to LPS become hyporesponsive to many other bacteria or bacterial products, they remain responsive to MDP. These data showing that MDP can act synergistically with another CSA inducer, can be injected repeatedly, and can stimulate mice unresponsive to LPS suggest potentially important in vivo applications.

Increased myelopoiesis during Leishmania major infection in mice: generation of 'safe targets', a possible way to evade the effector immune mechanism.

BALB/c mice are highly susceptible to Leishmania major infection and develop a disseminated lethal disease. Previous experiments indicate that during infection the spleen is heavily populated with large mononuclear cells containing amastigotes. Morphologically these cells resemble undifferentiated monocytes and granulocytes. In this study we examined myelopoiesis in BALB/c and C57BL/6 (resistant) mice during infection with L. major. The number of macrophage-granulocyte precursors in the spleen of infected BALB/c mice, determined by colony forming units in soft-agar cultures (cfu-c), increased steadily to a level of about 60 times that of normal sex- and age-matched controls. In C57BL/6 mice, spleen cfu-c peaked at about 1 month post-infection (four times that of normal controls) and declined thereafter to about two times normal levels. The number of cfu-c in the bone marrow did not change significantly in either strain during the infection. Colony stimulating activity (CSA) was found in supernates of cultures of adherent cells from the spleen of infected BALB/c mice. Under the same conditions, CSA was non-detectable in supernates of nonadherent spleen cells of infected mice, and those of adherent or nonadherent spleen cells of control animals. A possible role of undifferentiated macrophage-granulocytes in the exquisite susceptibility of BALB/c mice to L. major infection is discussed.

Stimulation of human endothelial cells by synthetic muramyl peptides: production of colony-stimulating activity (CSA).

The in vivo induction of colony-stimulating activity (CSA) by well-defined immunomodulatory synthetic muramyl peptides has been demonstrated recently in mice. In the present study, we tested the capacities of three muramyl peptides to induce CSA production in human endothelial cell (HEC) cultures. Two adjuvant-active peptides (MDP and Murabutide) induced CSA in the supernatant of cultured endothelial cells, whereas an adjuvant-inactive compound had no effect. This effect of MDP and Murabutide appeared to be time and concentration dependent and was not secondary to decreased production of inhibitors of colony formation. CSA secretion by stimulated HEC required de novo protein synthesis and did not result from the release of preformed active CSA. Maximal concentration appeared in the supernatant media within the first 24 h after addition of muramyl peptides, and a substantial second CSA secretion could be observed after a subsequent 24 h reexposure. This CAS was not dialyzable and promoted granulocyte-macrophage formation of nonadherent human marrow and unfractionated murine marrow. Our data demonstrate that the human endothelial cell is a target cell for MDP and Murabutide and suggest that in vivo endothelium might play an active role in muramyl peptide-induced modulation of hematopoiesis.

Colony-stimulating activity induced by synthetic muramyl peptides: variation with chemical structure and association with anti-infectious activity.

The in vivo induction of colony-stimulating activity (CSA) by N-acetylmuramyl-L-alanine-D-isoglutamine has been demonstrated recently. In this study we increased our understanding of this property by testing muramyl peptides of several structures and activities for their capacity to induce CSA in vivo. A comparison of the anti-infectious and adjuvant activities of these molecules revealed no correlation between the capacities of these compounds to be adjuvant active and to induce CSA: all adjuvant-inactive compounds induced CSA, and certain adjuvant-active molecules did not induce CSA. In contrast, all anti-infectious compounds induced CSA, but the reverse was not true; some compounds devoid of anti-infection activity were able to induce CSA only if they were adjuvant active.

Modulation of myelopoiesis in vivo by synthetic adjuvant-active muramyl peptides: induction of colony-stimulating activity and stimulation of stem cell proliferation.

Modulation of myelopoiesis by three synthetic muramyl peptides was investigated in vivo. Two adjuvant-active compounds (N-acetylmuramyl dipeptide [MDP] and MDP-butyl-ester) elicited significant responses in DBA/2 mice characterized by a rise in the level of monocyte-macrophage colony-stimulating activity in serum, a proliferation of multipotential stem cells in the bone marrow, and an expansion of granulocyte-macrophage progenitors in the spleen. In contrast, the adjuvant-inactive stereoisomer MDP(D-D) induced only low levels of circulating colony-stimulating activity. Thus, MDP or MDP-butyl-ester injection could induce a greater number of macrophages and therefore enhance both specific and nonspecific immunity.

Macrophage stimulation in vitro by an inactive muramyl dipeptide derivative after conjugation to a multi-poly(DL-alanyl)-poly(L-lysine) carrier.

It has been previously reported that N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP), which represents the minimal structure that can substitute for mycobacteria in Freund complete adjuvant, activated macrophages in vitro and in vivo. In the present study we show that, in contrast to MDP, the nonadjuvant MDP(DD) stereoisomer has no effect on cytostatic activity of thioglycolate-induced macrophages as measured by uptake of [3H]thymidine. However, surprisingly, after conjugation to an inert carrier, multi-poly(DL-alanyl)-poly(L-lysine), this compound activates macrophages in vitro and becomes at least as effective as MDP. It has also been shown in other studies that after conjugation MDP(DD) remained devoid of antigenicity and of adjuvant activity although such a conjugate could increase resistance to infection. It, therefore, appears that there exists no correlation between the structure required for adjuvant activity and the structure required for macrophage activation or for enhancement of nonspecific immunity.