Gunnar Habermann

Reproductive/developmental toxicity and immunotoxicity assessment in the nonhuman primate model.

Nonhuman primates are being used increasingly as a non-rodent animal model during preclinical toxicology and safety assessment on the basis of proven similarity and comparability between nonhuman primates and humans. The validity of the nonhuman primate models applies to many aspects of toxicological testing and holds particularly true for the evaluation of reproductive toxicology and developmental toxicology. More recently, the advent of humanized antibodies and vaccines imposed further demand on nonhuman primate models since many immunotherapeutics do not interact with rodent receptors but frequently only cross-react with primate tissue. In this paper we discuss the suitability of primate models for reproductive, developmental and immunotoxicology testing, and present our initial data on the development of lymphatic organs and immune system in a nonhuman primate model.

Cerebellar localization of the NO-receptive soluble guanylyl cyclase subunits-α2/β1 in non-human primates

Nitric-oxide-sensitive guanylyl cyclase (NO-sGC) plays a pivotal role in many second messenger cascades. Neurotransmission- and neuropathology-related changes in NO-sGC have been suggested. However, the cellular localization of NO-sGC in primate brains, including humans, remains unknown. Biochemical evidence has linked the α2-subunit of NO-sGC directly to neurotransmission in rodents. Here, we have used a recently characterized subunit-specific antibody for the localization of the α2-subunit on sections from the cerebelli of the common marmoset (Callithrix jacchus; New World monkey) and macaque monkeys (Macaca mulatta, M. fascicularis; Old World monkeys). In contrast to the more ubiquitous cytoplasmic presence of subunit-β1, the α2-subunit is mainly confined to the somato-dendritic membrane including the spines of the Purkinje cells. Only limited colocalization with presynaptically localized synaptophysin has been seen under our staining conditions, indicating a higher abundance of subunit-α2 at the postsynaptic site. This localization indicates that subunit-α2 links NO-sGC to neurotransmission, whereas subunit-β1 may act as a cytoplasmic regulator/activator by contributing to active heterodimer formation via translocation from the cytoplasm to the cell membrane. The last-mentioned action may be a prerequisite for generating nitric-oxide-dependent, subcellular, and postsynaptically localized cGMP signals along neuronal processes.

Spontaneous squamous cysts and squamous epithelial plaques in the heart of cynomolgus monkeys (Macaca fascicularis)

Squamous cysts and squamous epithelial plaques were observed in a total of seventeen cynomolgus monkeys. Eleven monkeys had squamous cysts, three of them also revealed squamous plaques and six revealed squamous plaques exclusively. At necropsy, cysts were recognized as yellow-white nodules with a smooth surface, that were located superficially along the interventricular septum, on the surface of the left ventricle or the apex of the heart. Microscopically, cysts were lined by a flattened epithelium and filled with keratin. Occasionally the epithelium was multi-layered or replaced by a rim of foreign body-type multinucleated giant cells. All animals with squamous cysts came from Mauritius, while those with squamous plaques came from Mauritius, China and Vietnam. As discussed in man, squamous cysts and plaques in cynomolgus monkeys are considered to represent displaced foregut epithelium, that was sequestered in the dorsal mesocardium prior to closure of the pleuropericardial fold during early embryologic development.

Müller glial cells of the primate foveola: An electron microscopical study

Abstract Previous studies on the ultrastructure of the primate foveola suggested the presence of an inverted cone‐like structure which is formed by 25–35 specialized Müller cells overlying the area of high photoreceptor density. We investigated the ultrastructure of the Müller cells in the foveola of a human and macaque retina. Sections through the posterior poles of an eye of a 40 years‐old human donor and an eye of an adult cynomolgus monkey (Macaca fascicularis) were investigated with transmission electron microscopy. The foveola consisted of an inner layer (thickness, 5.5–12 &mgr;m) which mainly contained somata (including nuclei) and inner processes of Müller cells; this layer overlaid the central Henle fibers and outer nuclear layer. The inner layer contained numerous watery cysts and thin lamelliform and tubular Müller cell processes which spread along the inner limiting membrane (ILM). The cytoplasm of the outer Müller cell processes became increasingly dispersed and electron‐lucent in the course towards the outer limiting membrane. The ILM of the foveola was formed by a very thin basal lamina (thickness, <40 nm) while the basal lamina of the parafovea was thick (0.9–1 &mgr;m). The data show that there are various conspicuous features of foveolar Müller cells. The numerous thin Müller cell processes below the ILM may smooth the inner surface of the foveola (to minimize image distortion resulting from varying light refraction angles at an uneven retinal surface), create additional barriers to the vitreous cavity (compensating the thinness of the ILM), and provide mechanical stability to the tissue. The decreasing density of the outer process cytoplasm may support the optical function of the foveola. HighlightsThe human and macaque foveola contains specialized Müller cells.The basal lamina of the ILM is very thin in the foveola.The inner foveolar layer contains somata and thin processes of the Müller cells.The outer Müller cell processes are increasingly electron‐lucent near the OLM.Foveolar Müller cells may have optical, barrier, and structural functions.

Comparison of cellular localisation of the Ca2+-binding proteins calbindin, calretinin and parvalbumin in the retina of four different Macaca species

Ca2+‐binding proteins are differentially expressed in the nervous system; their functional role often remains unclear. This immunohistochemical study aimed at characterising and comparing the expression pattern of the Ca2+‐binding proteins calbindin (Calb), calretinin (Calr) and parvalbumin (Parv) in the retina of four species of macaque monkeys: Macaca fascicularis (cynomolgus macaque), M. mulatta (rhesus macaque), M. thibetana (Tibetan macaque) and M. fuscata (Japanese macaque). Calb was found in cone photoreceptors and in a subset of bipolar cells. Calr was expressed in a subpopulation of amacrine cells. Parv was present in horizontal and ganglion cells. In addition, Müller cells were stained using antibodies against the specific marker cellular retinaldehyde‐binding protein (CRALBP). Immunostainings were used for calculation of the density of different cell populations. The expression pattern was similar between the examined species and between retinal regions.

Assessment of placental transfer and the effect on embryo-fetal development of a humanized monoclonal antibody targeting lymphotoxin-alpha in non-human primates.

An enhanced embryo-fetal development study was conducted in cynomolgus monkeys using pateclizumab, a humanized IgG1 monoclonal antibody (mAb) targeting lymphotoxin-alpha. Pateclizumab administration between gestation days (GD) 20 and 132 did not induce maternal or developmental toxicities. The ratio of fetal-to-maternal serum concentration of pateclizumab was 0.73% on GD 50 and 61% by GD 139. Decreased fetal inguinal lymph node-to-body weight ratio was present in the high-dose group without microscopic abnormalities, a change attributable to inhibition of lymphocyte recruitment, which is a pharmacologic effect of pateclizumab during late lymph node development. The effect was observed in inguinal but not submandibular or mesenteric lymph nodes; this was attributed to differential susceptibility related to sequential lymph node development. Placental transfer of therapeutic IgG1 antibodies; thus, begins during the first trimester in non-human primates. Depending on the potency and dose levels administered, antibody levels in the fetus may be pharmacologically or toxicologically relevant.