Welcome to the Jumping Frog Lab
Evolution of Immune Surveillance, Tumor and Viral Immunity
Current Research in the Jumping Frog Lab
Goyos A, Guselnikov S, Chida AS,
Sniderhan LF, Maggirwar SB,
Nedelkovska H, Robert J.
Involvement of nonclassical MHC
class Ib molecules in heat shock
responses. Eur J Immunol. 2007
The overall goal of our research is to understand the co-evolutionary aspects of selected molecules (e.g., heat shock proteins [hsps], hsp-receptors [CD91], NK cell receptors [KIR, FcRs], non-classical class Ib molecules [XNCs]) and their functions in innate and adaptive immunity against tumors and viruses. For this purpose, we use the frog, Xenopus laevis, which has proven to provide a unique and versatile model system. Some attributes of this model are: MHC class I deficient but immunocompetent larvae, T-cell-deficient thymectomized animals, minor and major histocompatibility-defined syngeneic clones, and MHC class I-negative and positive transplantable tumor cell lines, and a well-defined virus. Furthermore, our Xenopus experimental model has sufficient evolutionary distance from mammals to permit distinguishing species-specific adaptation or specialization from more fundamental and conserved features of the immune system.
One specific research area addresses the postulated dual role of heat shock proteins (hsps) in innate (signal of danger) and adaptive immunity (T-cell adjuvant). The Xenopus model offers the unique advantage of allowing one to study the immunological properties of hsps in the presence (adult) or absence (tadpole) of classical MHC class I-restricted antigen presentation and, as such, investigate a postulated more general role of hsps as components of an ancestral system of antigen presentation as well as danger signaling . A second area concerns the biological significance of immune cell effector that presents the dual features of adaptive (CD8 and T-cell receptors) and innate (NK receptors) immunity in defense against tumor and virus. This phylogenetic study of early mediators of cellular immunity is complemented by an extensive study of the molecular and genetic evolution of NK receptor families. A last research area concern basic and applied knowledge of viral immunity in amphibians using Xenopus and an iridovirus (FV3) as model.
Heat shock proteins and tumor immunity
X. laevis albinos mutants
We are investigating the postulated dual role of some heat shock proteins (hsps) as components of an ancestral system of immune surveillance involved in antigen presentation (adaptive immunity) as well as in danger signaling (innate immunity). Our Xenopus model allows us to study the immunological properties of hsps in the presence (adult) or absence (tadpole) of MHC class I presentation. We have shown that the ability of the hsp gp96 and hsp70 to chaperone antigenic peptides, to elicit potent specific cellular adaptive immune response and to interact with antigen-presenting cells, is phylogenetically conserved. We have obtained additional evidence of more complex immunomodulatory properties of hsps, involving NK and less well characterized CD8 T and/or NK/T cells. In particular Xenopus hsps generate potent immune responses against a tumor that does not express MHC class Ia molecules (a frequent immune escape mechanism). This tumor, however, expresses so-called non-classical class Ib mRNAs. We are testing the hypothesis that anti-tumor cytotoxic CD8 T cells generated by hsp immunization interact with class Ib surface molecules to kill tumor targets. The comparative tumor-immunity model we have developed in Xenopus will allow us to studie of the relationship between hsps and non-classical class Ib molecules that are postulated to act as indicators of intracellular stress and malignancy.
Evolution of hsp/hsp-receptor interactions
CD91, the endocytic receptor for a2-macroglobulin (a2-M), in mammals mediates the internalization of certain hsps and the cross-presentation of peptides they chaperone by antigen presenting cells. The phylogenetic conservation of the immunologically active CD91 ligands, a2-M and hsps, is consistent with the idea of an ancestral system of immune surveillance. We have further explored this hypothesis by taking advantage of Xenopus and asked how conserved is CD91 itself and whether the expression of CD91 is differentially modulated during immune responses between class I+ adult and naturally MHC class I-negative larvae. We have identified a Xenopus CD91 gene homologue that displays high sequence homology with other CD91 homologues. Phylogenetic analysis indicates that CD91 homologues branch as a monophyletic group distinct from other LDLRs; this suggests an origin of CD91 contemporary with metazoans. CD91 is expressed in most cell types including adult macrophages, B and T cells; as well as in splenocytes and thymocytes from naturally MHC class I negative larvae. CD91 is markedly up-regulated in vivo by adult peritoneal leukocytes following bacterial and viral stimulation; it is constitutively expressed on class I-negative larval peritoneal leukocytes at high levels and can not be further upregulated by such stimulation. These data are in agreement with a conserved role of CD91 in immunity.
Evolution of leukocyte Fc and Natural killer cell receptors
The families of leukocyte Fc receptors (FcR) and killer cell immunoglobulin-like receptors (KIRs) are important groups of surface molecules participating in adaptive and innate immunity whose phylogenetic history and relatedness is unknown. Our recent studies suggesting a role of NK cells and CD8 NK/T cells in Xenopus anti-tumor responses stimulated by hsps, make it important to learn more about the NK cell receptors that signal activation and inhibition of killing in this species. Indeed, a relationship between the immunomodulatory properties of hsps and Fc/NK receptors would be of major fundamental and clinical interest (hsp are currently being tested in cancer immunotherapy clinical trials). We are particularly interested in determining whether hsps can upregulate Fc/NK-receptors on certain leukocytes (i.e., NK cells and macrophages/dendritic cells) in Xenopus larvae and adults. If so, this would provide critical evidence of an important role of hsps as a bridge (both in the organism itself and during evolution) between innate and adaptive immunity. In collaboration with Alexander Taranin (Russia), we have identified in Xenopus a large (at least 20 members) and diverse family of FcR-like genes (designated XFLs), and we characterizing the expression, and function of the FcR-like proteins and signal co-receptors. Preliminary results suggest that a large proportion of XFL genes are silent in adults but strongly expressed at the metamorphic and larval stages. These genes may participate in regulatory mechanisms preventing autoimmunity during Xenopus metamorphosis.
Immune responses to emerging Ranaviral diseases
Electron microscopy of the heavily infected kidney
Although rapid progress has been made in identifying genes involved in innate (NK-receptor genes) and adaptive (TCR and MHC genes) immunity, very little is known about the roles and relative importance of innate and adaptive anti-viral immunity in ectothermic vertebrates. The recent realization that ranaviruses (Iridoviridae), may be causally contributing to the world-wide decline of amphibians lends urgency to understanding amphibian anti-viral immune defenses. We have recently established Xenopus as an important model to study immunity against emerging ranavirus infection in amphibians and evaluate the contribution of immunocompromised animals in the dissemination and progression of the diseases. Frog Virus 3 (FV3) is a large (120-200nm) dsDNA icosahedral virus. FV3 was originally isolated from the native North American leopard frog Rana pipiens, but FV3 or FV3-like viruses are now found worldwide in different genera and species, making it a potentially serious global threat to amphibians. We have shown: (1) that FV3 preferentially targets the kidney; (2) that adults resist high doses of FV3 by developing potent antibody (neutralizing IgG-equivalent IgY) and T cell responses (impaired by sublethal irradiation or CD8 T cell-depletion); and (3) that naturally MHC class I-deficient larvae are more susceptible than adults. These data establish Xenopus as a useful laboratory model system to further investigate fundamental mechanisms of viral immunity in ectothermic vertebrates and to better understand the role of host susceptibility factors in the actual emergence of viral pathogens.
Evolution of Activation-induced deaminase (AID)
In collaboration with Andrea Bottaro (Dept. of Medicine -Allergy/Immunology Unit), we have recently begun to study the structural and functional conservation of AID in Xenopus. Activation-induced deaminase (AID) is an activated B cell-specific cytidine deaminase enzyme required for both immunoglobulin class switch recombination (CSR) and somatic hypermutation (SHM). Phylogenetically, SHM appears early during vertebrate evolution, and is already detectable in elasmobranchs (e.g., sharks); by contrast. CSR is first found in amphibians. Since elucidating the evolutionary history of AID may provide important information regarding the origin of SHM and CSR we have cloned and characterized AID from Xenopus. Comparison of AID from Xenopus and other vertebrates will provide insights into protein regions critical for CSR and SHM, and into the origin of these unique mechanisms. Finally, the expression pattern of AID during immune responses will provide insight in process of B cell maturation in absence of germinal centers.