J Strohmaier | PubMed Health

PubMed2001

Kinetics and thermodynamics of beta 2-microglobulin binding to the alpha 3 domain of major histocompatibility complex class I heavy chain.

The major histocompatibility complex (MHC) class I molecule plays a crucial role in cytotoxic lymphocyte function. Functional class I MHC exists as a heterotrimer consisting of the MHC class I heavy chain, an antigenic peptide fragment, and beta2-microglobulin (beta2m). beta2m has been previously shown to play an important role in the folding of the MHC heavy chain without continued beta2m association with the MHC complex. Therefore, beta2m is both a structural component of the MHC complex and a chaperone-like molecule for MHC folding. In this study we provide data supporting a model in which the chaperone-like role of beta2m is dependent on initial binding to only one of the two beta2m interfaces with class 1 heavy chain. beta2-Microglobulin binding to an isolated alpha3 domain of the class I MHC heavy chain accurately models the biochemistry and thermodynamics of beta2m-driven refolding. Our results explain a 1000-fold discrepancy between beta2m binding and refolding of MHC1. The biochemical study of the individual domains of complex molecules is an important strategy for understanding their dynamic structure and multiple functions.

Animals↗

PubMed1985

Tubuloreticular inclusions in peripheral blood mononuclear cells related to systemic therapy with alpha-interferon.

Tubuloreticular inclusions (TRI) developed within the endoplasmic reticulum of peripheral blood mononuclear cells (PBMC) sampled from eight patients with chronic type B hepatitis during cycles of therapy with DNA-recombinant human alpha-interferon (rIFN alpha A). Each cycle of therapy consisted of a series of six intramuscular injections (triweekly) of a fixed dose of rIFN alpha A (from 18 to 68 X 10(6) IU/dose). In PBMC examined by transmission electron microscopy, TRI were absent prior to therapy and developed during therapy in all cases. Peak serum levels of alpha-interferon (320 to 960 IU/ml) were achieved within 12 hours. At 24 hours. TRI were detected in 0.5 to 6.5% of PBMC sections, and they persisted in 1.4 to 6.8% of sections examined at 48 hours. After five sequential interferon doses, TRI were observed in 1.6 to 9.8% of PBMC sections. TRI could no longer be detected at 5 to 16 days after cessation of rIFN alpha A, but they reappeared during subsequent cycles of therapy. Subpopulations of the PBMC with TRI were differentiated by immunoelectron microscopy utilizing a battery of anti-Leu monoclonal antibodies: surface markers of T cells, helper/inducer or cytotoxic/suppressor T cell subsets, natural killer cells, or B-cells were identified by direct or indirect procedures utilizing avidin and biotinylated peroxidase. In cases analyzed with multiple monoclonal antisera, TRI were expressed in all of the major PBMC subpopulations. Monocytes with TRI were demonstrated by the endogenous peroxidase reaction. TRI were not found in circulating polymorphonuclear granulocytes. Lymphocytes isolated from healthy donors and exposed to rIFN alpha A (100 IU/ml), for 48 to 72 hours in vitro, developed TRI in proportions of PBMC sections (2.3 to 8.4%) comparable to those observed in the interferon-treated patients. Stimulation of lymphocytes with concanavalin A, for 72 hours before rIFN alpha A exposure, enhanced formation of TRI which could then be found in T blasts. Stimulation of donor lymphocytes with Sendai virus, a potent inducer of alpha-interferon, also resulted in formation of TRI by 48 hours. This suggested that lymphocytotrophic virus infections could exercise a primary role in the natural pathogenesis of TRI.

Antibodies, Monoclonal↗

PubMedDate not supplied

The isolated major histocompatibility complex class I alpha3 domain binds beta2m and CD8alphaalpha dimers.

The MHC class I molecule plays a crucial role in cytotoxic lymphocyte function. The heavy chain of the MHC class I molecule can form many non-covalent interactions with other molecules on multiple domains and surfaces. We have generated an isolated alpha3 domain of a murine MHC class I molecule and evaluated the contribution of this domain to binding with the MHC class I light chain, beta2m, and CD8. The alpha3 domain binds beta2m at a thousand-fold higher concentration than the whole MHC, and binds CD8alphaalpha with a dependence on the alpha3 CD loop. Our results are relevant for models of MHC folding and CD8-MHC function. The study of individual domains of complex molecules is an important strategy for understanding their dynamic structure and function.

Binding Sites↗