Bernard Bizzini

Adjuvants — a balance between toxicity and adjuvanticity

Adjuvants have been used to augment the immune response in experimental immunology as well as in practical vaccination for more than 60 years. The chemical nature of adjuvants, their mode of action and the profile of their side effects are highly variable. Some of the side effects can be ascribed to an unintentional stimulation of different mechanisms of the immune system whereas others may reflect general adverse pharmacological reactions. The most common adjuvants for human use today are still aluminium hydroxide, aluminium phosphate and calcium phosphate although oil emulsions, products from bacteria and their synthetic derivatives as well as liposomes have also been tested or used in humans. In recent years monophosphoryl lipid A, ISCOMs with Quil-A and Syntex adjuvant formulation (SAF) containing the threonyl derivative of muramyl dipeptide have been under consideration for use as adjuvants in humans. At present the choice of adjuvants for human vaccination reflects a compromise between a requirement for adjuvanticity and an acceptable low level of side effects.

Tetanus toxin and botulinum A toxin inhibit release and uptake of various transmitters, as studied with particulate preparations from rat brain and spinal cord

SummaryThe effects of tetanus toxin and botulinum A toxin on the uptake and evoked release of various neurotransmitters were studied using particles from rat forebrain, corpus striatum and spinal cord. 1.Uptake. Tetanus toxin partially inhibits the uptake of glycine and choline into spinal cord synaptosomes. The effect on glycine uptake becomes statistically significant after a lag period of 60\2-120 min. It is no longer present when the toxin is heated, antitoxin-treated or toxoided. The inhibition by botulinum A toxin of choline uptake into spinal cord synaptosomes is weak but measurable, that of glycine uptake is at the borderline of detection.The uptake of GABA into forebrain cortex synaptosomes is slightly inhibited by tetanus toxin but hardly by botulinum A toxin. The effects of tetanus toxin and botulinum A toxin on the uptake of noradrenaline into striatal synaptosomes are negligible.2.Release. Tetanus toxin inhibits the potassium (25 mM) evoked release of radioactivity from rat forebrain cortex particles preloaded with labelled neurotransmitters. The sensitivity decreases in the following order: Glycine > GABA \2> acetylcholine. The toxin also inhibits the release of radioactivity from striatal particles preloaded with labelled noradrenaline. It is always 10\2-50 times more potent on spinal cord than on brain particles. The sensitivity of the evoked release from the spinal cord decreases in the order glycine > GABA > acetylcholine > noradrenaline.The toxin is identical with the causative agent because toxin-antitoxin complexes, toxoid and heated toxin do not influence the release from particles preloaded with glycine (spinal cord), GABA (forebrain) and noradrenaline (striatum).Botulinum toxin resembles tetanus toxin by its ability to diminish the release of radioactivity from preloaded forebrain (acetylcholine > GABA), striatal (noradrenaline), or spinal cord (glycine) particles. The botulinum toxin effect on the striatum (noradrenaline) and on the spinal cord (glycine) is due to its neurotoxin content.The identity of the toxin and the causative agent has been established by preheating and preincubation with antitoxin.It is proposed that a) tetanus and, however to a much lesser degree, botulinum A toxin act in a basically similar manner on a process underlying the function of synapses in general, and b) the pronounced sensitivity of glycine and GABA release from spinal cord, together with the axonal ascent of tetanus toxin, may be crucial in the pathogenesis of tetanus.

Involvement of Gangliosides in Rabies Virus Infection

The role of gangliosides in rabies virus infection of chick embryo-related (CER) cells was investigated. Cultured cells were pretreated with neuraminidase to render the cells transiently non-susceptible to viral infection. Incubation of these desialylated cells with gangliosides allowed them to incorporate exogenous gangliosides and they recovered their susceptibility to rabies virus infection. Infection of CER cells was monitored by specific fluorescence 24 h after virus inoculation. The use of individual purified gangliosides or mixtures of two gangliosides to restore cellular susceptibility to viral infection showed that GT1b and GQ1b were the most effective. The disialogangliosides were also active, principally GD1b, whereas GM1, GM3 were poorly active and GD3 inactive. Incubation of rabies virus with gangliosides prior to virus infection reduced the percentage of infected cells. The results indicate that highly sialylated gangliosides are part of the cellular membrane receptor structure for the attachment of infective rabies virus. However, it is possible that other glycoconjugates such as glycoproteins or glycolipids also participate as components of a receptor structure for rabies virus.

Experimental modification of postnatal cerebellar granule cell migration in vitro

Histotypic migration of [3H]thymidine pulse-labeled granule cell neurons in cerebellar folium explants was monitored in the presence of antibodies to cell adhesion molecules and quantified by automatic image analysis. When explants were cultured in the presence of monovalent antibody fragments to cell adhesion molecules L1 and N-CAM, an inhibition of cell migration of 33.3 +/- 4.4% and 13.9 +/- 2.1%, respectively, was observed. In the presence of an equimolar mixture of monovalent antibody fragments to L1 antigen and N-CAM no additive effects in inhibition of cell migration were seen. Antibodies to the L2 carbohydrate epitope which is common to L1, N-CAM and other cell surface glycoproteins showed a similarly small effect on cell migration as antibodies to N-CAM. Monoclonal antibodies to cell surface antigen M2 and polyclonal antibodies to mouse liver membranes reacting with the surface of all cerebellar cell types did not alter the migratory behavior of granule cells. Cultivation of explants in the presence of neuraminidase, ganglioside binding toxins, as well as glycosaminoglycans and glycosaminoglycan degrading enzymes, also did not modify the extent of cell migration under the culture conditions used.

Neurotropism of rabies virus. An in vitro study.

The relative susceptibility of neurons and glia, grown as monolayers in vitro, to rabies virus infection was explored. Established cell lines of neuronal or glial phenotype and primary cultures of cells derived from mouse dorsal root ganglia (DRG) or brain were used as homologues of the targets of rabies virus in the nervous system. Fixed rabies virus (CVS) strain was used in most experiments; other fixed rabies strains (PV, HEP, ERA) and a street rabies virus isolate were used in some. Virus-cell tropism was determined by immunofluorescence assay for rabies nucleocapsid antigen and cell permissivity was assessed by titration of virus yields. Neuronal cells always exhibited a much greater susceptibility to infection and a greater propensity to sustain viral growth. By immunofluorescence, 90–100% of neurons commonly had viral inclusion bodies, while doses of the virus three to four orders of magnitude higher still left >99% of astrocytes, in brain cell cultures and 90 ± 5% of the non-neuronal cells in DRG cultures without any obvious signs of rabies virus. Neuroblastoma cells (95 ± 5% with viral antigens) produced viral yields about four orders of magnitude higher than glioma cells (10 ± 5% with viral antigens). Though the overall infectivity of street virus was lower than that of fixed virus strains, a significantly higher viral tropism for neurons than for glia was maintained. Thus, primary neuronal cultures offer a means of exploring molecular events in rabies virus infection and their role in pathogenesis.

Use of the B-IIb tetanus toxin derived fragment as a specific neuropharmacological transport agent

It has been previously demonstrated that the non-toxic B-IIb tetanus toxin-derived fragment is transported retrogradely within neurons of the rat peripheral nervous system. In the present work we have shown that when a foreign polypeptide, in this case the Ibc tetanus toxin fragment, is coupled to B-IIb by a disulfide bond, it is transported retrogradely from the axonal endings within muscle to the motoneuronal perikarya. In contrast, Ibc fragment alone was found not to be transported. From these results we draw the conclusion that fragments like B-IIb may serve as specific carriers for chemical and chemotherapeutic agents into the central nervous system.

Neuronal acquisition of tetanus toxin binding sites: Relationship with the last mitotic cycle

In an earlier study on the developing nervous system, the existence of a temporal correlation between the appearance of tetanus toxin-binding cells and neurogenesis was reported (A. Koulakoff, B. Bizzini, and Y. Berwald-Netter (1982). Dev. Brain Res. 5, 139-147). Using a combined approach of immunocytochemistry and [3H]thymidine autoradiography it is shown that, in the fetal mouse central nervous system, dividing cells do not express membrane binding sites for tetanus toxin. A time-course quantitative autoradiography revealed that the toxin-binding sites become apparent within 7 +/- 1 hr, following the last S phase, on cells undergoing the conversion from dividing to postmitotic state. The acquisition of surface binding sites for tetanus toxin may thus be an early property of nascent central neurons, marking the transition from cycling precursor neuroblasts to postmitotic neuronal cells. Parallel studies on in vivo-developing dorsal root ganglia disclosed that at least some peripheral nervous system cells are endowed with tetanus toxin-binding capacity while still capable of DNA synthesis and undergo one or more divisions.

Transsynaptic retrograde labeling in the oculomotor system of the monkey with [125I]tetanus toxin BIIb fragment.

The injection of radioactive [125I]tetanus toxin BIIb fragment into the extraocular eye muscles of monkeys led to strong retrograde labeling of motoneurons. In addition, two patterns of weaker labeling were found: (1) discrete deposits of silver grains associated with cell soma, and (2) diffuse deposits unrelated to cell bodies. The discrete cell soma labeling was found in all areas known to make synaptic contact with the retrogradely filled motoneurons, and is indicative of transsynaptic retrograde transport. The use of tetanus toxin as a transsynaptic retrograde tracer substance is shown here for the first time at the light microscopic level.

A correlation between the appearance and the evolution of tetanus toxin binding cells and neurogenesis

The ontogenesis of cells expressing surface membrane binding sites for tetanus toxin (Tt) was studied in the mouse nervous system. Cells were labeled shortly after the tissue dissociation and the toxin bound was revealed by immunofluorescence. In the brain, spinal cord and dorsal root ganglia the toxin binding cells (TBC) are found as of very early stages of nervous system organogenesis, i.e. at 10 days of gestation. There is a close temporal correlation between the pattern of emergence and accumulation of TBC and the known pattern of appearance of post-mitotic neurons in mouse cerebral cortex, cerebellum and spinal cord. The curves of TBC abundance as a function of fetal age in various nervous system areas are different. They show regional fluctuations in the proportion of TBC that reflect the cumulative changes in the dynamics of neuronal subpopulations. The results indicate that Tt can be used as an ontogenetically early marker of neuronal differentiation and that the acquisition of Tt receptors may represent one of the earliest detectable characteristics of the developing neurons.

Papain-derived fragment IIc of tetanus toxin: its binding to isolated synaptic membranes and retrograde axonal transport

The papain-derived fragment IIc of tetanus toxin, which is immunologically identical to the B-IIb fragment, has previously been shown to bind gangliosides. As could be expected from its analogy with the B-IIb fragment, the IIc fragment was also found to bind to isolated synaptic membranes and to be transported retrogradely from the axonal endings within muscle to the motoneuronal perikarya. It is concluded that the IIc fragment--like the B-IIb fragment--might also serve as a specific carrier for chemical and chemotherapeutical agents into the central nervous system.