Biomedical subjects

A Llera

Publications and source records attributed to A Llera.

6 recordsLinked to original sources

PubMed1999

The structural basis of T cell activation by superantigens.

Superantigens (SAGs) are a class of immunostimulatory and disease-causing proteins of bacterial or viral origin with the ability to activate large fractions (5-20%) of the T cell population. Activation requires simultaneous interaction of the SAG with the V beta domain of the T cell receptor (TCR) and with major histocompatibility complex (MHC) class II molecules on the surface of an antigen-presenting cell. Recent advances in knowledge of the three-dimensional structure of bacterial SAGs, and of their complexes with MHC class II molecules and the TCR beta chain, provide a framework for understanding the molecular basis of T cell activation by these potent mitogens. These structures along with those of TCR-peptide/MHC complexes reveal how SAGs circumvent the normal mechanism for T cell activation by peptide/MHC and how they stimulate T cells expressing TCR beta chains from a number of different families, resulting in polyclonal T cell activation. The crystal structures also provide insights into the basis for the specificity of different SAGs for particular TCR beta chains, and for the observed influence of the TCR alpha chain on SAG reactivity. These studies open the way to the design of SAG variants with altered binding properties for TCR and MHC for use as tools in dissecting structure-activity relationships in this system.

Amino Acid Sequence↗

PubMed1998

A mutational analysis of the binding of staphylococcal enterotoxins B and C3 to the T cell receptor beta chain and major histocompatibility complex class II.

The three-dimensional structure of the complex between a T cell receptor (TCR) beta chain (mouse Vbeta8.2Jbeta2.1Cbeta1) and the superantigen (SAG) staphylococcal enterotoxin C3 (SEC3) has been recently determined to 3.5 resolution. To evaluate the actual contribution of individual SAG residues to stabilizing the beta-SEC3 complex, as well as to investigate the relationship between the affinity of SAGs for TCR and MHC and their ability to activate T cells, we measured the binding of a set of SEC3 and staphylococcal enterotoxin B (SEB) mutants to soluble recombinant TCR beta chain and to the human MHC class II molecule HLA-DR1. Affinities were determined by sedimentation equilibrium and/or surface plasmon detection, while mitogenic potency was assessed using T cells from rearrangement-deficient TCR transgenic mice. We show that there is a clear and simple relationship between the affinity of SAGs for the TCR and their biological activity: the tighter the binding of a particular mutant of SEC3 or SEB to the TCR beta chain, the greater its ability to stimulate T cells. We also find that there is an interplay between TCR-SAG and SAG-MHC interactions in determining mitogenic potency, such that a small increase in the affinity of a SAG for MHC can overcome a large decrease in the SAG's affinity for the TCR. Finally, we observe that those SEC3 residues that make the greatest energetic contribution to stabilizing the beta-SEC3 complex ("hot spot" residues) are strictly conserved among enterotoxins reactive with mouse Vbeta8.2, thereby providing a basis for understanding why SAGs having other residues at these positions show different Vbeta-binding specificities.

Amino Acid Sequence↗

PubMed1998

Three-dimensional structure of the complex between a T cell receptor beta chain and the superantigen staphylococcal enterotoxin B.

Superantigens (SAGs) are a class of immunostimulatory proteins of bacterial or viral origin that activate T cells by binding to the V beta domain of the T cell antigen receptor (TCR). The three-dimensional structure of the complex between a TCR beta chain (mouse V beta8.2) and the SAG staphylococcal enterotoxin B (SEB) at 2.4 A resolution reveals why SEB recognizes only certain V beta families, as well as why only certain SAGs bind mouse V beta8.2. Models of the TCR-SEB-peptide/MHC class II complex indicate that V alpha interacts with the MHC beta chain in the TCR-SAG-MHC complex. The extent of the interaction is variable and is largely determined by the geometry of V alpha/V beta domain association. This variability can account for the preferential expression of certain V alpha regions among T cells reactive with SEB.

Animals↗

PubMed1998

Structure-function studies of T-cell receptor-superantigen interactions.

Superantigens (SAGs) are a class of disease-causing and immunostimulatory proteins of bacterial or viral origin that activate T cells by binding to the V beta domain of the T-cell antigen receptor (TCR). The three-dimensional structure of the complex between a TCR beta chain (mouse V beta 8.2-J beta 2.1-C beta 1) and the SAG staphylococcal enterotoxin C3 (SEC3) has been recently determined. The complementarity-determining region 2 (CDR2) of the beta chain and, to lesser extents, CDR1 and hypervariable region 4 (HV4) bind in a cleft between the small and large domains of the SAG. A model of the TCR-SAG-peptide/MHC complex constructed from available crystal structures reveals how the SAG acts as a wedge between the TCR and MHC, thereby displacing the antigenic peptide away from the TCR and circumventing the normal mechanism for T-cell activation by peptide/MHC. To evaluate the actual contribution of individual SAG residues to stabilizing the V beta C beta-SEC3 complex, as well as to investigate the relationship between the affinity of SAGs for TCB and MHC and their ability to activate T cells, we measured the binding of a set of SEC3 mutants to a soluble recombinant TCR beta chain and to the human MHC class II molecule HLA-DR1. We show that there is direct correlation between affinity and ability to stimulate T cells, with SAGs having the highest affinity for the TCR being the most biologically active. We also find that there is an interplay between TCR-SAG and SAG-MHC interactions in determining mitogenic potency, such that a small increase in the affinity of a SAG for MHC can overcome a large decrease in the SAG's affinity for the TCR. Finally, we observe that those SEC3 residues that make the greatest energetic contribution to stabilizing the V beta C beta-SEC3 complex are strictly conserved among enterotoxins reactive with mouse V beta 8.2, thereby explaining why SAGs having other residues at these positions show different V beta-binding specificities.

Amino Acid Sequence↗

PubMed1989

[Neutrophil-dependent inflammatory reactions in systemic lupus erythematosus].

We studied the possible role of polymorphonuclear neutrophil (PMN) aggregation in Systemic Lupus Erythematosus (SLE) by the capacity of sera from 32 lupus patients to induce in vitro normal PMN aggregation. Neutrophil aggregating activity (NAA) in this group was significantly greater than that found in 8 inactive SLE patients and in 8 controls. In patients with SLE, there was a positive correlation between disease severity and the quantitative measure of NAA. High levels of NAA were particularly characteristic of central nervous system SLE. These data suggest that the formation of intravascular leukoaggregates may contribute to morbidity in SLE. Normal PMN increase their spontaneous superoxide anion production (0.21 nmol/min 10(7) PMN) when stimulated with sera from SLE patients. Lupus PMN also show an enhancement of 100% in superoxide production in vitro when stimulated with lupus sera. When N formyl methionine leucyl phenylalanine (FMLP) was used, lupus PMN showed an O2-production of 2.1 nmol/min 10(7) which is 5-fold the response of normal PMN stimulated by FMLP. Our results show the existence of seric factors in SLE patients that can stimulate O2-production by PMN. Lupus neutrophils show an increased response to membrane stimuli such as FMLP, capable of triggering the respiratory burst. Lupus neutrophils appear more responsive membrane stimuli such as FMLP, capable of triggering the respiratory burst. Lupus neutrophils appear more responsive to membrane stimuli. The seric and the cellular factors seem to indicate an increased rate of superoxide production by PMN in SLE patients, which can be relevant to vasculitis and tissue damage.

Adult↗

PubMedDate not supplied

Increased superoxide production by polymorphonuclear leukocytes in systemic lupus erythematosus.

Normal and lupus PMN show an enhancement in superoxide production in vitro when stimulated with lupus serum. When N-formyl-methionyl-leucyl-phenylalanine (FMLP) was used, lupus PMN showed an O2- production of 2.1 nmol/min/10(7) cells, which is 5.2 times the response of normal PMN stimulated by FMLP. Our results show the existence of serum factors in SLE patients that can stimulate O2- production by PMN. Lupus neutrophils showed an increased response to membrane stimuli such as FMLP, capable of triggering the cell respiratory burst. Lupus neutrophils appeared more responsive to membrane stimuli. The serum and cellular factors seemed to indicate an increase rate of superoxide production by PMN in lupus patients, which could be relevant factors in the development of vasculitis and tissue damage.

Chemotactic Factors↗