Immunology Letters, 44 (19951 67-74 0165-2478/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved IMLET 2260 Class II cytoplasmic and transmembrane domains are not required for class II-mediated B cell spreading William F. Wade a,*, Dion K. Dickrnan a, Daniel Peterson a, James McCluskey b, Irina Khrebtukova a ’ School of Biological Science, University of Nebraska-Lincoln, Lincoln, NE 68588-0118, USA bFlinders Medical Centre, Department of Clinical Immunology, Bedford Park, SA 5042, Australia (Received 3 August 1994; revised 28 September 1994; accepted 30 September 1994) Key words: B cell; MHC class II; Actin; Signal transduction; Antigen presentation; Cytoskeleton 1. Summary B cells cultured on immobilized anti-class II mono- clonal antibody (mAb) change from round to flattened cells, with lamellipodia and filopodia. This change in cell morphology, termed ‘spiders’, occurs within 30 min upon culture and is mediated through either I-A or I-E molecules. Class II molecules that are defective in mediating protein kinase C (PKC) due to the deletions of both (Y and j3 chain’s cytoplasmic (Cy) domain sequences can induce spider formation. B-cell transfec- tants that express chimeric MHC class II/class I molecules, where the ectodomains are class II se- quences and the transmembrane and Cy domains are class I sequences also form spiders when cultured on anti-class II mAb. The spider morphology is not in- duced by either anti-immunoglobulin (Ig) or anti-MHC class I mAb. Treatment of B cells to increase intracellu- lar CAMP, a component of the class II signaling path- way also results in spider formation with the same kinetics and percent change in the responding popula- tion as that induced by anti-class II mAb. Cytochalasin A treatment which disrupts cytoskeletal actin filaments and the tyrosine kinase inhibitor, genistein, both inhibit spider formation. Actin redistributes from a concentric ring in round cells to the ends of the filopodia in the spiders. The mechanism of spider induction whether resultant from second messengers following class II * Corresponding author: (current address) Dartmouth Medical School, Department of Microbiology, Borwell Bldg., 630W Lebanon, NH 03756, USA. Tel.: (603) 650-6896; Fax: (603) 650-6223. Abbreviations: Ag, Antigen; APC, antigen-presenting cell; Cy, cyto- plasmic; db CAMP, dibutyryl CAMP; Ig, immunoglobulin; MHC, major histocompatibility complex; mAb, monoclonal antibody; PKC, protein kinase C. signaling or from non-signaling-induced physical inter- actions of class II with intracellular cytoskeletal compo- nents only requires the extracellular domains of class II. The biologic relevance of B-cell spiders is currently not known but has been reported to be associated with class II signal transduction and efficient Ag presentation. 2. Introduction The ability of cells to change shape in response to various stimuli has been explained in biologic terms as being required for the effector function of the cell. Cyclic AMP is a well-known modulator of cell mor- phology. Some of the effects include an increase in astrocyte process growth, antagonism of growth pro- grams in dividing lymphocytes and stop migration sig- nals in polymorphonuclear cells [l-3]. The change in cell morphology is mediated mainly through changes in the cytoskeletal architecture, by either decreasing or increasing actin polymerization [4-lo]. It is currently appreciated that many of these changes in the cell are mediated after specific receptor ligation. The effect of CAMP is thought mainly to be exerted by CAMP-de- pendent PKA, which in some system regulates the phosphorylation state of myosin light-chain kinase, an enzyme which modulates myosin’s ability to interact with actin [lo]. Another potential way for CAMP to modulate cytoskeleton is for actin to be phosphorylated via CAMP-dependent PKA [4]. MHC class II molecules composed of an (Y and p chain, are receptors on APC that serve a dual purpose: presentation of peptide Ag to T lymphocytes and gener- ation of intracellular signals to the B lymphocyte, a specialized APC 111-181. These signals to the APC SSDI 0165-2478(94)00178-2 67