Biomedical subjects

J I Krieger

Publications and source records attributed to J I Krieger.

12 recordsLinked to original sources

PubMed2003

In vitro evidence that subcutaneous administration of glatiramer acetate induces hyporesponsive T cells in patients with multiple sclerosis.

Glatiramer acetate (GA; Copaxone) is a random sequence polypeptide used in the treatment of relapsing remitting multiple sclerosis (RR MS). We have recently demonstrated that prior to treatment, GA induces proliferation of resting T cells and is not cross-reactive with myelin antigens. Daily GA injections induce a significant loss of this GA responsiveness, which is associated with the induction of highly cross-reactive Th2-type T cells potentially capable of suppressing inflammatory responses. The mechanism of action by which GA induces T cell nonresponsiveness leading to T cell receptor degeneracy in patients with RR MS is unknown. Here, we examined the effects of daily GA administration on the induction of T cell hyporesponsiveness. The frequency of GA-reactive T cells in peripheral blood of seven patients with RR MS was measured by limiting dilution analysis prior to and during 6 months of treatment. In addition, a model in which GA-reactive T cells were stimulated in vitro was developed to better characterize the selection of T cell populations over time. In vivo treatment with GA induced a decrease in GA-reactive T cell frequencies and hyporesponsiveness of CD4(+) T cell reactivity to GA in vitro that was only partially reversed by the addition of IL-2. These data suggest that T cell peripheral tolerance to GA was achieved in vivo during treatment. Thus, our in vitro data suggest that the underlying changes in GA-reactive CD4(+) T cell reactivity could be explained by the induction of T cell anergy and clonal elimination.

Adult↗

PubMed2001

Immunological memory: contribution of memory B cells expressing costimulatory molecules in the resting state.

Traditionally, emphasis has been placed on the roles of Th cells in generating and amplifying both cellular and humoral memory responses. Little is known about the potential contributions of B cell subsets to immunological memory. Resting memory B cells have generally been regarded as poor APC, attributed in part to the relative paucity of costimulatory molecules identified on their surface. We describe a novel subpopulation of human memory B cells that express CD80 in their resting state, are poised to secrete particularly large amounts of class switched Igs, and can efficiently present Ag to and activate T cells. This functionally distinct B cell subset may represent an important mechanism by which quiescent human B cells can initiate and propagate rapid and vigorous immune memory responses. Finally, these studies extend recent observations in the murine system and highlight the phenotypic and functional diversity that exists within the human B cell memory compartment.

Antigen Presentation↗

PubMed2001

Malignant glioma cells use MHC class II transactivator (CIITA) promoters III and IV to direct IFN-gamma-inducible CIITA expression and can function as nonprofessional antigen presenting cells in endocytic processing and CD4(+) T-cell activation.

Malignant gliomas (MGs), lethal human central nervous system (CNS) neoplasms, contain tumor infiltrating lymphocytes (TIL). Although MHC class II molecules are frequently detected on MG cells, suggesting that they may be capable of antigen (Ag) presentation to CD4(+) T cells, deficiencies in CD4(+) T-cell activation are associated with these nonimmunogenic tumors. We evaluated regulation of the MHC class II transactivator (CIITA), the key intermediate that controls class II expression, in MG cells and tested whether MG cells could process native Ag. After interferon-gamma (IFN-gamma) stimulation, MG cells upregulated CIITA and class II molecules. IFN-gamma-inducible CIITA expression in MG cells, as well as primary human astrocytes, was directed by two CIITA promoters, pIV, the promoter for IFN-gamma-inducible CIITA expression in nonprofessional antigen-presenting cells (APC), and pIII, the promoter that directs constitutive CIITA expression in B cells. Both pIII and pIV directed CIITA transcription in vivo in MGs and ex vivo in IFN-gamma-activated primary MG cultures. We also demonstrate for the first time that MG cells can process native Ag for presentation to CD4(+) MHC class II-restricted Th1 cells, indicating that MG cells can serve as nonprofessional APC. CIITA may be a key target to modulate MHC class II expression, which could augment immunogenicity, Ag presentation, and CD4(+) T-cell activation in MG therapy.

Adult↗

PubMed2000

Human and murine CD4 T cell reactivity to a complex antigen: recognition of the synthetic random polypeptide glatiramer acetate.

The capacity of glatiramer acetate (GA), a random copolymer of alanine, lysine, glutamic acid, and tyrosine to stimulate primary in vitro human and murine T cell proliferation was examined. PBMCs isolated from healthy humans and relapsing remitting multiple sclerosis patients and spleen cells from inbred strains of mice, expressing different H-2 haplotypes, were used as sources of non-GA-primed lymphocytes. GA functioned as a universal Ag, inducing dose-dependent proliferation of all non-GA-primed human and murine T cell populations tested. Moreover, GA stimulated PBMCs derived ex vivo from human cord blood, strongly suggesting that GA can activate both naive and memory T cells. The human T cell proliferative responses to GA were HLA class II DR-restricted by virtue of the ability of anti-class II Ab to inhibit T cell proliferation, and the demonstration that individual GA specific human T cell clones were HLA class II DR-restricted by either restriction element but not both. Furthermore, GA-reactive T cells secreted Th0 cytokines and expressed a diverse repertoire of TCR. Limiting dilution analysis indicated that the T cell precursor frequency among the healthy human adults tested ranged from 1:5,000 to 1:125,000. Given that all of the T cell populations tested were isolated from non-GA-primed donors, it appears that virtually all humans and murine strains contain significant numbers of T cell populations cross-reactive with GA. These findings may explain the recent clinical finding that daily s.c. administration of GA ameliorates the progression of multiple sclerosis.

Adult↗

PubMed2000

Glatiramer acetate (Copaxone) induces degenerate, Th2-polarized immune responses in patients with multiple sclerosis.

We examined the effect of glatiramer acetate, a random copolymer of alanine, lysine, glutamic acid, and tyrosine, on antigen-specific T-cell responses in patients with multiple sclerosis (MS). Glatiramer acetate (Copaxone) functioned as a universal antigen, inducing proliferation, independent of any prior exposure to the polymer, in T-cell lines prepared from MS or healthy subjects. However, for most patients, daily injections of glatiramer acetate abolished this T-cell response and promoted the secretion of IL-5 and IL-13, which are characteristic of Th2 cells. The surviving glatiramer acetate-reactive T cells exhibited a greater degree of degeneracy as measured by cross-reactive responses to combinatorial peptide libraries. Thus, it appears that, in some individuals, in vivo administration of glatiramer acetate induces highly cross-reactive T cells that secrete Th2 cytokines. To our knowledge, glatiramer acetate is the first agent that suppresses human autoimmune disease and alters immune function by engaging the T-cell receptor. This compound may be useful in a variety of autoimmune disorders in which immune deviation to a Th2 type of response is desirable.

Adult↗

PubMed1997

Changes in cytokine secretion induced by altered peptide ligands of myelin basic protein peptide 85-99.

Myelin basic protein (MBP)-specific T cells were isolated directly from peripheral blood by stimulation either with native MBPp85-99 or altered peptide ligands (APLs) in which substitutions of the lysine were made at position 93, a TCR contact residue. We report here that the APL 93A could alter the cytokine profile of some autoreactive MBPp85-99 reactive T cell clones, switching them from a Th0 phenotype secreting high concentrations of IL-4, IL-5, and IFN-gamma into Th2 cells secreting significantly less IFN-gamma. However, in vitro stimulation with the 93A peptide, in some instances, induced T cells that responded better to the native MBPp85-99 peptide. Functionally, the APL 93A was shown to act as an antagonist for IFN-gamma secretion. Based on TCR sequencing and single cell cloning, this alteration in cytokine profile was determined to be the result of the differential activation of individual T cell clones. We discuss the implications of these data for the strength of signal model of T cell activation.

Autoimmune Diseases↗

PubMed1994

Definition of a DQ3.1-specific binding motif.

A quantitative peptide binding assay using purified DQA1*0301/DQB1*0301 (DQ3.1) molecules was developed and validated by examining the correlation between the data obtained in the binding assay with those obtained in inhibition of Ag presentation assays. By the combined use of large libraries of synthetic peptides and of substitution and truncation analogues, a putative DQ3.1 motif was defined. Its most prominent feature is the requirement for two small and/or hydrophobic residues spaced at positions i + 2 and i + 4. This motif is quite different from the motif recognized by DR molecules, but similar to the motif previously defined for certain IA alleles (the putative mouse homologue of DQ). These data suggest that various class II isotypes have evolved to present different peptide structures to each other, thus maximizing the repertoire of different epitopes available to T cell scrutiny.

Amino Acid Sequence↗

PubMed1993

Human anti-endotoxin antibody HA-1A mediates complement-dependent binding of Escherichia coli J5 lipopolysaccharide to complement receptor type 1 of human erythrocytes and neutrophils.

HA-1A has been shown clinically to decrease mortality in septic patients with gram-negative bacteremia. In this study, the ability of HA-1A to augment the serum complement-dependent immune adherence of 125I-labeled Escherichia coli J5 lipopolysaccharide (LPS) to human erythrocytes (RBC) and polymorphonuclear leukocytes (PMNL) was evaluated. In vitro studies indicated three things: HA-1A mediates immune adherence of 125I-J5 LPS to human RBC and PMNL in a dose-dependent manner; under these conditions, high concentrations of LPS (400 ng/mL) could be specifically bound. Immune adherence occurs via the classical complement pathway as demonstrated by its calcium dependence; HA-1A-J5 LPS-C' immune complexes bound to CR1 on human RBC and PMNL. PMNL binding and internalization of immune complexes was demonstrated by trypsin stripping of externally bound immune complexes. These studies support the proposal that HA-1A can lower the bioavailability of endotoxin by mediating binding and potential clearance of LPS via human RBC through the reticuloendothelial system or via direct internalization by peripheral blood PMNL.

Antibodies, Monoclonal↗

PubMed1991

Single amino acid changes in DR and antigen define residues critical for peptide-MHC binding and T cell recognition.

Single amino acid substitutions of Ag and MHC were used to analyze the fine structure of the influenza hemagglutinin (HA)-derived epitope (HA 307-319) recognized in the context of DR7 molecules by a T cell clone. Putative T cell (HA 308, 310, 311, 313, and 316) and DR (HA 309, 312, and 317) contact residues of the Ag were identified by the use of single amino acid-substituted analogs that were tested for their T cell-activating and DR-binding capacities. The peptide-DR7-T cell interaction was further characterized by the use of a panel of 13 site-directed DR7 mutant transfectants analyzed for their capacity to present Ag to T cells, and for their purified mutant DR7 molecules to bind HA 307-319 or its single amino acid-substituted analogs. Eight mutants lost their Ag-presenting function, whereas only one had any decrease in peptide binding. Finally, for three of the mutants it was possible to correct the deleterious effects of mutation by using a particular single amino acid-substituted analog of the peptide molecule. The observed pattern of complementation led to a model that predicts that the Ag assumes an extended conformation, with a turn, in the binding groove, such that the following residues are in close proximity: DR 86-HA 309, DR 71-HA 312, DR 30-HA 314, and 315.

Amino Acid Sequence↗

PubMed1991

MHC-antigen-T cell interactions: an overview.

We describe the establishment and validation, both at the biochemical and biological levels, of direct assays to measure the interactions between synthetic peptides and purified HLA class II molecules. The results of several independent approaches to define the structural requirements for the interaction of peptide-class II molecules are also described. Such approaches include random screening, sequence analysis, and site-directed mutagenesis. Finally, in vivo data illustrating the possibility that the competition at the level of the interactions between autoantigenic peptides and class II molecules could be a useful tool in the treatment of T cell-mediated autoimmune diseases are presented.

Autoimmune Diseases↗

PubMed1986

Capacity of B cells to function as stimulators of a primary mixed leukocyte reaction.

The capacity of B cells to serve as stimulator cells for a primary mixed leukocyte reaction (MLR) was evaluated. Percoll-fractionated B cells were stimulated with lipopolysaccharide and dextran sulfate (L/D) or a B cell stimulatory factor (BSF-1)-containing culture supernatant, and then were fixed before being used as stimulator cells to more precisely define the state of activation associated with MLR stimulatory capacity. It was found that unstimulated B cells or B cells stimulated for 1 day with L/D or BSF-1 were incapable of initiating a primary MLR, whereas B cells incubated for 3 days in L/D were potent stimulators. The differential activity of 1 day L/D- and BSF-1-activated B cells compared with 3 day L/D-activated B cells was not related to the amount of the relevant MHC class I or class II alloantigens on these cell populations, because all three groups had large increments in MHC class II expression in the following order: BSF-1 greater than 3 day L/D greater than 1 day L/D, and had little difference in MHC class I expression. Also, all three populations were capable of stimulating both MHC class I- and class II-specific T cell hybrids. It was concluded that the capacity of 3 day L/D-activated cells to stimulate a primary MLR was due to the elaboration of necessary co-stimulator molecules. We evaluated whether interleukin 1 (IL 1) was the co-stimulator involved. That this was not the case was indicated by two findings. First, 3 day-activated L/D cells failed to express IL 1 activity as measured by a highly sensitive IL 1 assay that utilizes the T cell line D10.G4.1. Second, recombinant IL 1 added to MLR cultures containing 1 day L/D- or BSF-1 activated B cells failed to function as a co-stimulator. In contrast, the phorbol ester PMA was a potent co-stimulator in this system. We conclude from these experiments that appropriately activated B cells can function as stimulators of a primary MLR, and that they elaborate critical co-stimulator molecules, distinct from IL 1, that enable them to function in this regard.

Animals↗

PubMed1985

Antigen presentation by splenic B cells: resting B cells are ineffective, whereas activated B cells are effective accessory cells for T cell responses.

In this study, we have investigated the ability of splenic B cells to act as antigen-presenting cells. Previous data had established that lipopolysaccharide (LPS)-activated B cells were effective antigen-presenting cells; however, the relative capacity of resting B cells to carry out this function remains controversial. Splenic B cells from naive BALB/c mice were depleted of macrophages, dendritic cells, and T cells, and were fractionated on the basis of cell density by using Percoll gradient centrifugation. Fractions were collected from the 50/60, 60/65, and 65/72% interfaces and from greater than 72% (pellet). Cytofluorograph analysis of the fractionated B cells showed that the two lower density fractions (50/60 and 60/65) contained a number of cells which, by cell size determination, appeared to be activated B cells, whereas the two higher density fractions (65/72 and greater than 72) appeared to contain predominantly small resting B cells contaminated by many fewer activated B cells. Functionally, the capacity of fractionated B cells to act as accessory cells for a concanavalin A response or present the antigens chicken ovalbumin (OVA) or OVA-tryptic digest gave similar results, which indicated a striking hierarchy of accessory cell function in the different Percoll fractions. When normalized to the most active low-density fraction (50/60%), the activity of the other fractions were: 60/65 = 78%; 65/72 = 25%; and greater than 72 = 4%. The differences in the functional capacity between the various Percoll fractions did not appear to be due to differences in Ia expression. Although the expression of Ia varied approximately 12-fold within any one fraction, there was little difference in the mean amount of Ia on cells obtained from the various fractions. Kinetic studies showed that activation of B cells with LPS and dextran sulfate resulted in the expression of two stages of functional development. The first stage was an increased efficiency of accessory cell function that was abrogated by irradiation with 4000 rad followed by a second stage, which was characterized by the acquisition of resistance to treatment with 4000 rad. When nonfractionated B cells that had been stimulated with LPS and DexSO4 were sorted on the basis of cell size into a small B cell fraction and a large B cell fraction, only the large B cells were able to present antigen. Taken together, these data suggest that much of the accessory cell function associated with splenic B cells can be accounted for by the relatively small percentage of activated B cells present in the spleen.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗