RESUMEN
Antibodies can mediate injury of organ transplants by several mechanisms, including complement activation and interaction with Fc receptors on cells. We tested the hypothesis that antibodies could also cause up-regulation of complement receptors on cells to increase the responses to complement activation by interaction with split products of C3. In our experimental model, B10.A (H-2(a)) cardiac transplants survive significantly longer in C57BL/6 (H-2(b)) immunoglobulin knockout recipients (IgKO) than in their wild-type counterparts. Passive transfer of specific antibodies to donor MHC class I to IgKO recipients of cardiac allografts at the time coinciding with a vigorous cellular infiltration reconstituted acute rejection. We tested the effects of alloantibodies on CR1/2 expression by alloantigen-stimulated T cells. Both CD4(+)/CR1/2(+) and CD8(+)/CR1/2(+) populations of T cells were expanded in C57BL/6 splenocytes stimulated by B10.A alloantigen in 7-day MLR after coculture with endothelial cells sensitized with IgG1 and IgG2b mAb specific to MHC. Endothelial cells sensitized with antibodies also caused an expansion of CD8(+) T cells expressing CR1/2 in lymph node lymphocytes harvested from a C57BL/6 recipient of a B10.A cardiac allograft. These data suggest that antibodies can augment the cellular rejection process through expanding the population of T cells interacting with complement split products.
Asunto(s)
Trasplante de Corazón/inmunología , Isoantígenos/farmacología , Receptores de Complemento 3b/genética , Receptores de Complemento 3d/genética , Linfocitos T/inmunología , Animales , Línea Celular , Endotelio Vascular , Citometría de Flujo , Ganglios Linfáticos/inmunología , Ratones , Ratones Endogámicos C3H , Ratones Endogámicos C57BL , Ratones Noqueados , Linfocitos T/efectos de los fármacosRESUMEN
While activated T cells are known to have enhanced biological responses to antigen stimulation, the biophysical basis of this increased sensitivity remains unknown. Here, we show that, on activated T cells, the TCR avidity for peptide-MHC complexes is 20- to 50-fold higher than the TCR avidity of naive T cells. This increased avidity for peptide-MHC depends on TCR reorganization and is sensitive to the cholesterol content of the T cell membrane. Analysis of the binding data indicates the enhanced avidity is due to increases in cross-linking of TCR on activated T cells. Activation-induced membrane (AIM) changes in TCR avidity represent a previously unrecognized means of increasing the sensitivity of activated T cells to small amounts of antigen in the periphery.
Asunto(s)
Activación de Linfocitos , Receptores de Antígenos de Linfocitos T/metabolismo , Linfocitos T/inmunología , Animales , Membrana Celular/inmunología , Membrana Celular/metabolismo , Colesterol/metabolismo , Reactivos de Enlaces Cruzados , Dimerización , Antígenos H-2/química , Antígenos H-2/metabolismo , Técnicas In Vitro , Cinética , Lípidos de la Membrana/metabolismo , Ratones , Modelos Moleculares , Péptidos/metabolismo , Estructura Cuaternaria de Proteína , Receptores de Antígenos de Linfocitos T/química , Linfocitos T/metabolismoRESUMEN
T cell receptors (TCR) and major histocompatibility complex (MHC) molecules are integral membrane proteins that have central roles in cell-mediated immune recognition. Therefore, soluble analogs of these molecules would be useful for analyzing and possibly modulating antigen-specific immune responses. However, due to the intrinsic low-affinity and inherent solubility problems, it has been difficult to produce soluble high-affinity analogs of TCR and class II MHC molecules. This report describes a general approach which solves this intrinsic low-affinity by constructing soluble divalent analogs using IgG as a molecular scaffold. The divalent nature of the complexes increases the avidity of the chimeric molecules for cognate ligands. The generality of this approach was studied by making soluble divalent analogs of two different classes of proteins, a TCR (2C TCR2Ig) and a class II MHC (MCCI-Ek2Ig) molecule. Direct flow cytometry assays demonstrate that the divalent 2C TCR2Ig chimera retained the specificity of the native 2C TCR, while displaying increased avidity for cognate peptide/MHC ligands, resulting in a high-affinity probe capable of detecting interactions that heretofore have only been detected using surface plasmon resonance. TCR2IgG was also used in immunofluorescence studies to show ER localization of intracellular peptide-MHC complexes after peptide feeding. MCCI-Ek2Ig chimeras were able to both stain and activate an MCC-specific T cell hybridoma. Construction and expression of these two diverse heterodimers demonstrate the generality of this approach. Furthermore, the increased avidity of these soluble divalent proteins makes these chimeric molecules potentially useful in clinical settings for probing and modulating in vivo cellular responses.
Asunto(s)
Antígenos de Histocompatibilidad Clase II/metabolismo , Receptores de Antígenos de Linfocitos T/metabolismo , Proteínas Recombinantes de Fusión/metabolismo , Secuencia de Bases , Dimerización , Antígenos de Histocompatibilidad Clase II/química , Humanos , Hibridomas/inmunología , Inmunoglobulina G/metabolismo , Activación de Linfocitos , Datos de Secuencia Molecular , Receptores de Antígenos de Linfocitos T/química , Proteínas Recombinantes de Fusión/químicaRESUMEN
Understanding the regulation of cell surface expression of specific peptide-major histocompatibility complex (MHC) complexes is hindered by the lack of direct quantitative analyses of specific peptide-MHC complexes. We have developed a direct quantitative biochemical approach by engineering soluble divalent T cell receptor analogues (TCR-Ig) that have high affinity for their cognate peptide-MHC ligands. The generality of this approach was demonstrated by specific staining of peptide-pulsed cells with two different TCR-Ig complexes: one specific for the murine alloantigen 2C, and one specific for a viral peptide from human T lymphocyte virus-1 presented by human histocompatibility leukocyte antigens-A2. Further, using 2C TCR- Ig, a more detailed analysis of the interaction with cognate peptide-MHC complexes revealed several interesting findings. Soluble divalent 2C TCR-Ig detected significant changes in the level of specific antigenic-peptide MHC cell surface expression in cells treated with gamma-interferon (gamma-IFN). Interestingly, the effects of gamma-IFN on expression of specific peptide-MHC complexes recognized by 2C TCR-Ig were distinct from its effects on total H-2 Ld expression; thus, lower doses of gamma-IFN were required to increase expression of cell surface class I MHC complexes than were required for upregulation of expression of specific peptide-MHC complexes. Analysis of the binding of 2C TCR-Ig for specific peptide-MHC ligands unexpectedly revealed that the affinity of the 2C TCR-Ig for the naturally occurring alloreactive, putatively, negatively selecting, complex, dEV-8-H-2 Kbm3, is very low, weaker than 71 microM. The affinity of the 2C TCR for the other naturally occurring, negatively selecting, alloreactive complex, p2Ca-H-2 Ld, is approximately 1000-fold higher. Thus, negatively selecting peptide-MHC complexes do not necessarily have intrinsically high affinity for cognate TCR. These results, uniquely revealed by this analysis, indicate the importance of using high affinity biologically relevant cognates, such as soluble divalent TCR, in furthering our understanding of immune responses.