A study of complexes of class II invariant chain peptide: major histocompatibility complex class II molecules using a new complex-specific monoclonal antibody.

Complexes of major histocompatibility complex (MHC) class II molecules containing invariant chain (Ii)-derived peptides, known as class II-associated invariant chain peptides (CLIP), are expressed at high levels in presentation-deficient mutant cells. Expression of these complexes in mutant and wild-type antigen-presenting cells suggests that they represent an essential intermediate in the MHC class II antigen-presenting pathway. We have generated a monoclonal antibody, 30-2, which is specific for these complexes.

Truncation of the class II beta-chain cytoplasmic domain influences the level of class II/invariant chain-derived peptide complexes.

Previous studies have established that antigen presenting cells (APC) expressing major histocompatibility complex class II beta chains with truncated cytoplasmic domains are impaired in their capacity to activate T cells. While it had been widely accepted that this impairment is due to a defect in class II cytoplasmic domain-dependent signal transduction, we recently generated transgenic mice expressing only truncated class II beta chains, and functional analyses of APC from these mice revealed signaling-independent defects in antigen presentation. Here, we demonstrate that T cells primed on such transgenic APC respond better to stimulation by APC expressing truncated beta chains than by wild-type APC.

Endogenous peptides associated with MHC class II and selection of CD4 T cells.

CD4 T cells undergo positive and negative selection during thymic development mediated by the interaction of T-cell receptors with MHC class II molecules expressed by thymic epithelial cells and bone marrow-derived antigen presenting cells in the thymus. The majority of MHC molecules are occupied with peptides derived from self proteins. Although the role of self peptides in the negative selection of CD4 cells is well established, the influence of peptides on positive selection of CD4 T cells remained elusive.

Requirement for peptide in alloreactive CD4+ T cell recognition of class II MHC molecules.

To examine the role of peptide in alloreactive class II MHC-restricted responses, we transfected I-A molecules into the Ag-processing defective mutant cell line, T2. Consistent with their defective Ag-processing phenotype, the T2 transfectants predominantly express SDS-unstable I-A molecules on their surface. These cells and phenotypically normal APCs were used to study primary and secondary alloreactive T cell responses in limiting dilution assays.

Intracellular assembly and transport of endogenous peptide-MHC class II complexes.

To define the intracellular site of assembly of endogenous peptide-MHC class II complexes, an immunochemical approach was undertaken employing a monoclonal antibody specific for an endogenous peptide-class II complex in combination with subcellular fractionation. Here, we show that newly synthesized MHC class II molecules, upon exit from the Golgi, are delivered into a dense endocytic compartment (MIIC) distinct from late endosomes and lysosomes. Endogenous peptide-class II complexes are initially formed in this compartment and subsequently traffic through late endosomal vesicles prior to cell surface expression.

T and B cell receptors discriminate major histocompatibility complex class II conformations influenced by the invariant chain.

Direct recognition of major histocompatibility complex (MHC) molecules may occur when T cells are positively selected in the thymus and also during recognition of non-self MHC molecules. Since peptide recognition and binding of particular monoclonal antibodies is strongly influenced by the invariant chain (Ii) of the class II molecule, we have asked whether Ii also affects recognition of non-self MHC molecules by T cells. We find that Ii binding alters MHC class II conformation as detected by a monoclonal antibody, and that this alteration is retained in cell surface MHC class II molecules after Ii dissociates.

Monoclonal antibody detection of a major self peptide. MHC class II complex.

MHC class I and class II molecules transport foreign and self peptides to the cell surface and present them to T lymphocytes. Detection of these peptide:MHC complexes has thus far been limited to analysis of the response of a T cell. Previously, we showed that a mAb, Y-Ae, reacts with 10 to 15% of class II molecules on peripheral B lymphocytes and on cells in the thymus medulla but not thymus cortex in mice that express both I-Ab and I-Eb molecules.

Sequence analysis of peptides bound to MHC class II molecules.

CD4 T cells recognize peptide fragments of foreign proteins bound to self class II molecules of the major histocompatibility complex (MHC). Naturally processed peptide fragments bound to MHC class II molecules are peptides of 13-17 amino acids which appear to be precessively truncated from the carboxy terminus, perhaps after binding to the MHC class II molecule. The finding of predominant self peptides has interesting implications for antigen processing and self-non-self discrimination.

Presentation of endogenous immunoglobulin determinant to immunoglobulin-recognizing T cell clones by the thymic cells.

Using immunoglobulin (Ig)-recognizing T helper clones the expression of Ig peptide/major histocompatibility complex class II complexes derived by the processing of endogeneous Ig molecules in the thymus was demonstrated. It was found that thymic B cells but not "classic" thymic antigen-presenting cells and macrophages represent the major antigen-presenting cell type of determinants of endogenously synthesized surface Ig (Ig kappa-1b) and anti-surface Ig antibodies (IdC3B9). The Ig kappa-1b-presenting activity in the thymus appears relatively late, only after 3 weeks of postnatal life, while in the spleen an efficient presentation of endogenous Ig kappa-1b epitope is observed very early after birth.

Immunoglobulin-specific T-B cell interaction. IV. B cell presentation of idiotypic determinant(s) of monoclonal anti-surface immunoglobulin antibody to idiotope-recognizing helper T clones.

Previously, we have demonstrated T-B cell interactions mediated by T cell recognition of immunoglobulin (Ig) peptide/major histocompatibility complex (MHC) class II complexes derived by the B cell processing of endogenously synthesized Ig molecules. In this report Ig-specific T-B cell interaction mediated by B cell presentation of idiotopes (Id) of anti-sIg antibodies to Id-specific T cell clones has been studied in Ig kappa-1-congenic rat strains. A panel of August (RT-1c; Ig kappa-1a) rat T helper clones specific for Id of syngeneic anti-Ig kappa-1b C3B9 monoclonal antibody (mAb) has been developed to study IdC3B9 presentation by Ig kappa-1b-bearing B cells from congenic August.

Immunoglobulin-specific T-B cell interaction. III. B cell activation by immunoglobulin-recognizing T cell clones.

Immunoglobulin (Ig)-specific T-B cell interactions were studied in the model of T cell recognition of Ig kappa chain Ig kappa-1b allotype in Ig kappa-1-congenic rats. Using Ig kappa-1b-recognizing major histocompatibility complex (MHC)-restricted T helper clones from August rats we have shown that Ig kappa-1b+ B cells from congenic August.1b rats presented Ig kappa-1b epitope of the processed self-synthesized Ig to T clones.

Immunoglobulin-specific T-B cell interaction. II. T cell clones recognize the processed form of B cells' own surface immunoglobulin in the context of the major histocompatibility complex class II molecule.

In the preceding report (Eur. J. Immunol.

Immunoglobulin-specific T-B cell interaction. I. Presentation of self immunoglobulin determinants by B lymphocytes.

Immunoglobulin (Ig)-specific T-B cell interactions have been studied in the model of T cell recognition of the kappa chain Ig kappa-1b allotype in Ig kappa-1-congeneic rat strains. An efficient presentation of endogenous Ig allotypic determinants by irradiated spleen cells from (WAG.1b x August)F1 (RT-1u/c; Ig kappa-1b/1a) rats to Ig kappa-1b-specific lymph node T cells from Ig kappa-1-congeneic (WAG x August)F1 (RT-1u/c; Ig kappa-1a) rats was demonstrated.