Immunobiology 219 (2014) 341–349 Contents lists available at ScienceDirect Immunobiology jo ur nal ho me page: www.elsevier.com/locate/imbio Altered receptor binding densities in experimental antiphospholipid syndrome despite only moderately enhanced autoantibody levels and absence of behavioral features Katrin Frauenknecht a,∗,1 , Aviva Katzav b,1 , Christina Grimm a , Joab Chapman b , Clemens J. Sommer a a Department of Neuropathology, University Medical Center of the Johannes Gutenberg University Mainz, 55131 Mainz, Germany b Department of Neurology, Chaim Sheba Medical Center, Sackler Faculty of Medicine, Tel Aviv University, 52621 Tel Hashomer, Israel a r t i c l e i n f o Article history: Received 18 September 2013 Received in revised form 19 November 2013 Accepted 20 November 2013 Available online 28 November 2013 Keywords: Antiphospholipid antibody level Antiphospholipid syndrome Behavior In vitro receptor autoradiography Neurotransmitter receptor 5-HT 1A receptor a b s t r a c t Experimental antiphospholipid syndrome (eAPS) in Balb/c mice causes neuropsychiatric abnormalities including hyperactivity, increased explorative behavior and cognitive deficits. Recently, we have demon- strated that these behavioral changes were linked to an upregulation of serotonergic 5-HT 1A receptor binding densities in cortical and hippocampal regions while excitatory and inhibitory neurotransmitter receptors remain largely unchanged. To examine whether the observed behavioral features depend on a critical antibody concentration, mice with only moderately enhanced antiphospholipid antibodies (aPL), about 50–80% of high levels, were analyzed and compared to controls. The staircase test was used to test animals for hyperactivity and explorative behavior. The brains were analyzed for tissue integrity and inflammation. Ligand binding densities of NMDA, AMPA, GABA A , 5-HT 1A , M1 and M2 muscarinic acetyl- choline receptors, respectively, were analyzed by in vitro receptor autoradiography and compared to brains of mice from our previous study with high levels of aPL. Mice with only moderately enhanced aPL did not develop significant behavioral changes. Brain parenchyma remained intact and neither inflam- mation nor glial activation was detectable. However, there was a significant decrease of NMDA receptor binding densities in the motor cortex as well as an increase in M1 binding densities in cortical and hippocampal regions, whereas the other receptors analyzed were not altered. Lack of neuropsychiatric symptoms may be due to modulations of receptors resulting in normal behavior. In conclusion, our results support the hypothesis that high levels of aPL are required for the manifestation of neuropsy- chiatric involvement while at lower antibody levels compensatory mechanisms may preserve normal behavior. © 2013 Published by Elsevier GmbH. Abbreviations: aCL, anti-cardiolipin-antibodies; AMPA, -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid; aPL, antiphospholipid antibodies; APS, antiphospho- lipid syndrome; aPS, anti-phosphatidylserine-antibodies; BBB, blood-brain barrier; beta2-GPI, beta2-glycoprotein I; CD, cluster of differentiation; CFA, conjugated Freund’s adjuvant; CL, cardiolipin; DAB, diaminobenzidine; DG, dentate gyrus; eAPS, experimental APS; CNS, central nervous system; Foxp3, forkhead box P3; GABA, gamma- aminobutyric acid; GBS, Guillain–Barré syndrome; GFAP, glial fibrillary acidic protein; H&E, hematoxylin eosin; Iba1, ionized calcium binding adaptor molecule 1; IHC, immunohistochemistry; IR, immunoreactivity; mAChR, muscarinic acetylcholine receptor; M1, primary motor cortex; NMDA, N-methyl-d-aspartate; OD, optical den- sity; PBS, phosphate-buffered Saline; PBST, phosphate-buffered Saline + Tween 20; PFA, paraformaldehyde; ROI, regions of interest; SD, standard deviation; SLE, systemic lupus erythematosus; S1, primary somatosensory cortex; S2, secondary somatosensory cortex; TBS, Tris-buffered saline; TBST, tris-buffered Saline + Tween-20; TESPA, triethoxysilylpropylamine; TIA, transient ischemic attack; TNFalpha, tumor necrosis factor alpha; 5-HT, 5-hydroxytryptamin. ∗ Corresponding author at: Department of Neuropathology, University Medical Center of the Johannes Gutenberg University Mainz, Langenbeckstrasse 1, 55131 Mainz, Germany. Tel.: +49 6131 174332; fax: +49 6131 176606. E-mail address: katrin.frauenknecht@unimedizin-mainz.de (K. Frauenknecht). 1 These authors contributed equally. 0171-2985/$ – see front matter © 2013 Published by Elsevier GmbH. http://dx.doi.org/10.1016/j.imbio.2013.11.006