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E Mellins

Publications and source records attributed to E Mellins.

11 recordsLinked to original sources
PubMed1991

Rapid signaling to B cells by antigen-specific T cells requires CD18/CD54 interaction.

This study reports early B and T cell signaling events during cognate interactions between a human B cell line pulsed with peptide and an Ag-specific T cell clone. As has been previously reported, peptide in the context of the appropriate class II molecule stimulated a rise in intracellular calcium [Ca2+]i in the Ag-specific T cell clone. The activation of the T cell clone was associated with a reciprocal rise in [Ca2+]i in the B cells. Engagement of receptors on the B cell surface by the T cell also was associated with inositol phospholipid turnover comparable to that elicited by stimulation through sIg. Early signaling events in B cells can therefore be stimulated in cognate interactions with Ag-specific T cells, without the direct engagement of Ig receptors. A class II deficient B lymphoblastoid mutant, 6.1.6, which was incapable of presenting peptide to the T cell clone, could be stimulated to produce a rise in [Ca2+]i if the T cell clone was activated by monoclonal antibodies to CD3. Therefore, the interaction of class II molecules on the B cell with the TCR and/or the CD4 accessory molecule was not essential for T-dependent B cell activation. However, T-dependent signalling of B cells was profoundly inhibited by mAb to CD18 (beta-chain of LFA-1) on the T cell or CD54 (ICAM-1) on the B cell, demonstrating the importance of this pair of adhesion molecules in early T-B cell interactions.

Antigens, CD↗
PubMed1991

A gene required for class II-restricted antigen presentation maps to the major histocompatibility complex.

We have previously described a set of mutants (16.23-selected mutants) of a B lymphoblastoid cell line that are defective in the presentation of intact proteins to class II-restricted T cells, but effectively present immunogenic peptides. The mutations in these mutants are recessive in somatic cell hybrids and are not in Class II structural genes. Here, we report on a unique mutant, 5.2.4, in which a similar defect in class II-restricted antigen presentation has occurred in association with a one-megabase homozygous deletion in the class II region of the major histocompatibility complex (MHC). The defects in class II presentation among three of the 16.23-selected mutants, and between these mutants and 5.2.4, are noncomplementary in somatic cell hybrids. This suggests that the class II presentation-defective phenotype in all four mutants results from lesions in a single MHC-linked gene, a conclusion strengthened by the finding that in a hybrid made with a second, unrelated MHC deletion mutant, T2, the class II presentation defect in a 16.23-selected mutant is also not complemented. Mutant 5.2.4, in addition to its class II presentation defect, is also defective in surface expression of MHC class I molecules, most likely because its deletion encompasses the peptide supply factor 1 gene, whose function is known to be required for normal abundance of cell surface class I molecules. However, the surface abundance of class I molecules is normal in the 16.23-selected mutants, suggesting that the lesions affecting class I surface abundance and class II presentation result from mutations in different genes.

Antigen-Presenting Cells↗
PubMed1991

Mutations affecting antigen processing impair class II-restricted allorecognition.

Both exogenously derived and endogenously derived Ag generally require processing for their optimal binding and presentation by class I and class II major histocompatibility proteins. It is not known whether steps involved in Ag processing also affect the recognition of alloreactive T cells. We have recently described B cell mutants which have general defects in the processing and presentation of a variety of exogenous Ag to class II restricted T cells. In this report we have studied the ability of these processing mutants to stimulate a set of anti-DR3-specific alloreactive T cells clones. These processing/presentation mutants express normal MHC class II molecules, both in terms of primary sequence and cell surface abundance, but they appear unable to generate effective peptide-MHC complexes. When tested for their ability to stimulate MHC class II alloreactive T cell clones, only one of four T cell clones was stimulated by these mutants; the other three alloreactive T cell clones were not stimulated by either of two different mutants. Both of these mutants express normal levels of the accessory molecules, LFA-3 and ICAM-1. The inability of these mutants to stimulate three of four alloreactive clones indicates that the capacity to be recognized by many alloreactive T cells is linked to the Ag processing capacity of a stimulator cell.

Antigen-Presenting Cells↗
PubMed1991

Psychosomatic musculoskeletal pain in childhood: clinical and psychological analyses of 100 children.

The clinical and psychological findings on 100 children with psychosomatic musculoskeletal pain seen at a major pediatric rheumatology referral center are reported. Most (76%) were female, median age was 13 years, and median duration of symptoms was 1 year. Multiple painful sites were common (66%). The pain was constant (63%) or intermittent (37%); 45% had hyperesthesia, and almost all maintained a cheerful affect when complaining of severe pain. Two predominant abnormal family milieu were seen. One was cohesive, stable, and organized, but intolerant of separation and individuation. The other was chaotic, emotionally unsupportive, with high levels of conflict. Members of the cohesive family type reported significantly less distress than members of chaotic families. Enmeshment between mother and child was common in both family types. Although frequently viewed as bright, most of these children had normal intelligence, and some had unrecognized academic difficulty. These children, compared with those with arthritis, had a significantly lower global well-being score. Clinical depression was unusual (11%). Most (97%) responded favorably to intensive physical and occupational therapy along with individual or family psychotherapy; 78% become symptom free or fully functional. Children with these signs and symptoms should have full psychological evaluations and respond well to treatment directed toward decreasing pain and restoring function.

Adolescent↗
PubMed1990

Defective processing and presentation of exogenous antigens in mutants with normal HLA class II genes.

Presentation of an exogenous protein antigen to helper (CD4+)T-lymphocytes by antigen presenting cells (APC) generally requires that the APCs degrade the native protein antigen into an immunogenic peptide, a process termed 'antigen processing', and that this peptide bind to a major histocompatibility complex (MHC) class II molecule. The complex of peptide and MHC molecule on the APC surface provides the stimulatory ligand for the alpha beta T cell receptor. The intracellular pathways and molecular mechanisms involved in the generation of the peptide-MHC complex are not well understood. Here, we describe several mutant APCs which are altered in their ability to present native exogenous protein antigens but effectively present immunogenic peptides derived from these proteins. The lesions in these mutants are not in the class II structural genes, but they affect the conformation of mature class II dimers.

Antigen-Presenting Cells↗
PubMed1990

Point mutations define positions in HLA-DR3 molecules that affect antigen presentation.

Allelic differences in major histocompatibility complex (MHC)-encoded class II molecules affect both the binding of immunogenic peptides to class II molecules and the recognition of MHC molecule-peptide complexes by T cells. As yet, there has been no extensive mapping of these functions to the fine structure of human class II molecules. To determine sites on the HLA-DR3 molecule involved in antigen presentation to T cells, we used monoclonal antibodies specific for HLA-DR3 to immunoselect mutants of a B-lymphoblastoid line. We located the sites of single amino acid substitutions in the HLA-DR3 molecule and correlated these structural changes with patterns of recognition by HLA-DR3-restricted, antigen-specific T cells, allospecific T cells, and allospecific anti-DR3 monoclonal antibodies. We analyzed seven mutations. One mutation, at position 74 in domain 1 of the DR beta chain, affected recognition by all T cells tested, whereas others, at positions 9, 45, 73, 151, and 204 of the DR beta chain and position 115 of the DR alpha chain, altered recognition by some T cells, but not others. Each of the substitutions resulted in a unique pattern of T-cell stimulation. In addition, each T-cell clone recognized a different subset of the mutants. These results indicate that different residues of the DR3 molecule are involved in presentation of antigen to different DR3-restricted T cells. These studies further show that substitutions which most likely affect peptide binding alter recognition of DR3 molecules by an alloreactive T-cell clone and some allospecific antibodies.

Alleles↗
PubMed1989

mRNA abundance, rather than differences in subunit assembly, determine differential expression of HLA-DR beta 1 and -DR beta 3 molecules.

The class II major histocompatibility molecules HLA-DR are formed by the association of a single DR alpha chain with two nonallelic DR beta chains. In DR3 cells one DR beta chain is severalfold more abundant than the other. We have studied the mechanism that controls the differential expression of these DR beta genes. We determined the amino-terminal sequences of the two expressed DR beta chains. Comparison of these sequences with the nucleotide sequences of the DR3B1 and DRB3a genes indicates that the abundant chain is the B1 gene product. Supporting this conclusion, an informative mutant, 9.4.3, was found to have lost the abundant beta chain and beta 1 mRNA. This mutant expresses normal cell surface levels of the DR beta 3 chain and exhibits no significant dosage compensation of its beta 3 chain. The unchanged level of DR beta 3 dimer on the cell surface suggests that free DR alpha chains are not the limiting factor in the surface expression of the beta 3 chain and, further, that the differential regulation of the surface expression of the two DR beta chains occurs at a step prior to DR assembly. Quantitation of DR beta mRNAs by locus-specific oligonucleotide probes showed that beta 1 mRNA is 4.5-fold more abundant than beta 3 mRNA, strongly indicating that the greater surface expression of DR beta 1 is a direct consequence of greater beta 1 mRNA abundance.

Cell Line↗
PubMed1988

A single amino acid substitution in the human histocompatibility leukocyte antigen DR3 beta chain selectively alters antigen presentation.

Activation of T lymphocytes by immunogenic peptides bound to HLA molecules is a central event in the generation of an immune response. To determine the sites on HLA molecules involved in this process, we isolated mutant EBV-transformed B cell clones that express altered HLA-DR3 molecules. One mutant has lost the ability to stimulate a T cell clone specific for a mycobacterial protein, but retains the ability to stimulate other antigen-specific T cells. The DNA sequence of the complete DR alpha and beta coding regions revealed a single nucleotide change resulting in a glutamic acid to lysine substitution at amino acid 9 in the first hypervariable region of the DR beta chain. These results are discussed in relation to a recently proposed model of class II molecule structure.

Amino Acid Sequence↗
PubMed1987

Importance of HLA-DQ and -DP restriction elements in T-cell responses to soluble antigens: mutational analysis.

We describe a new approach to delineating the restriction elements used by antigen-specific human T-cell lines. EBV-transformed B cell lines and congenic HLA class II antigen-loss mutants are used to present soluble antigen to immune T cells. In this way it is possible to assess the independent contribution of individual class II loci to the restriction repertoire of the T cells. In contrast to results obtained with other methods of restriction element analysis, we find that approximately 40% of the T-cell response to several antigens is restricted by non-DR class II molecules. Both mutational analysis and blocking by class II specific monoclonal antibodies demonstrate that the non-DR restricted responses derive from DQ and DP-encoded determinants. We also find specific DR/DQ haplotype preferences for the presentation of some but not all antigens. Using a mutant that expresses only the DQ1 molecule, and is derived from a DR1, DQ1 parent line, we demonstrate a functional split of serologically defined DQ1 molecules consistent with the electrophoretic variation reported between DQ1 molecules linked to DR1 and those linked to DR2. Pairs of mutants that differ by expression of a single class II protein reveal a much broader use of available class II restriction elements than previously recognized.

Antibodies, Monoclonal↗
PubMedDate not supplied

A gene in the human major histocompatibility complex class II region controlling the class I antigen presentation pathway.

Major histocompatibility complex (MHC) class I molecules export peptides to the cell surface for surveillance by cytotoxic T lymphocytes. Intracellular peptide binding is critical for the proper assembly and transport of class I molecules. This mechanism is impaired as a result of a non-functional peptide supply factor gene (PSF) in several human mutant cell lines with genomic lesions in the MHC. We have now identified PSF in the MHC class II region by deletion mapping in mutants and chromosome-walking. PSF is homologous to mammalian and bacterial ATP-dependent transport proteins, suggesting that it operates in the intracellular transport of peptides.

Amino Acid Sequence↗