DNA sequence of the mouse H-2Dd transplantation antigen gene

The inbred BALB/c mouse has three transplantation antigens, H2-Kd, H2-Ld, and H2-Dd. We present the complete nucleotide sequence of the H2-Dd gene as well as 777 residues of previously unpublished H-2Dd protein sequence. These data complete the sequences of all the BALB/c transplantation antigen genes and permit detailed comparison with each other and with their counterparts from the inbred C57BL/10 mouse. Transplantation antigens may differ from one another by as much as 5%-15% of their amino acid sequence for the external domains. These extensive differences may arise by gene conversion. The H-2D region of the BALB/c mouse encodes the H2-Dd and the H2-Ld genes. Serologic data suggest that at least two additional transplantation antigen molecules, H2-Rd and H2-Md, are encoded in the H-2D region of the major compatibility complex. Paradoxically, gene cloning studies have only identified the H2-Dd and the H2-Ld genes in the H-2D region. A complete DNA sequence of the H2-Dd gene shows that a variety of alternative splice sites exist throughout the gene, which may lead to additional gene products and may explain the multiplicity of H-2D-encoded polypeptides

Subset-specific co-stimulatory signals are required for IL-2 production but not growth inhibition responses by T cell hybrids specific for myelin basic protein

Two distinct types of T cell hybridomas (designated THYB-1 and THYB-2) were derived by fusing BW5147 thymoma cells with encephalitogenic T helper cells from Lewis rats. Both subsets required MHC-restricted presentation of determinants within the 72-86 peptide sequence of myelin basic protein (MBP) as a requisite signal for IL-2 production. Unlike THYB-1 hybrids, however, THYB-2 hybrids required additional accessory cell activities that were mediated by radiosensitive nonadherent (RS-NAdh) splenocytes (SPL). In this study, we describe two observations indicating that RS-NAdh SPL enable MBP-specific responses of THYB-2 hybrids by providing subset-specific co-stimulatory signals that act independently of antigen recognition pathways. First, RS-NAdh SPL were required by THYB-2 hybrids for MBP-stimulated IL-2 production but were not needed when MBP-specific inhibition of hybrid growth was used as an alternative measure of cellular activation. Second, PMA and ionomycin induced optimal IL-2 production by both tHYB-1 hybrids and BW5147 thymoma cells but only stimulated low or marginal levels of IL-2 production by THYB-2 hybrids. Together, these observations indicate that RS-NAdh SPL were required for the specific response of IL-2 production regardless of whether the response was stimulated by antigen or by mitogens that bypass initial antigen recognition events. This study thereby provides additional evidence that distinct stimulus-response relationships define two T-helper cell lineages in experimental autoimmune encephalomyelitis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30179/1/0000564.pd

Unexpected complexity of the dm1 mutation revealed in the structure of three H-2D/L-related antigens

The H-2L dm1 and H-2D dm1 MHC antigens of the B10.D2 ( H-2 dm1 ) mutant mouse strain (formerly known as M504 or H-2 da ) have been compared to the H-2L d and H-2D d antigens of the B10.D2 ( H-2 d ) mouse strain. L dm1 and L d are 45 000 M r antigens and both are reactive with anti-H-2.“28” ( k/r anti- h2 ) serum and unreactive with anti-H-2.4 ( k/b anti- a ) serum which detects private determinants of the D dm1 and D d antigens. However, the tryptic peptide compositions of these two antigens are different and, based on the number of major tryptic peptides which coelute during ion-exchange chromatography, the estimated peptide homology between L dm1 and L d is 80 percent. A newly defined antigen (M r = 39 000), designated gp39 dm1 , was found in glycoprotein extracts of the dm1 strain but not of the d strain. This antigen coprecipitates with L dm1 but does not coprecipitate with D dm1 indicating that it lacks the H-2.4 determinant. In comparison with L dm1 , gp39 dm1 appears to contain far fewer Arg and Lys residues and is most likely not a simple proteolytic fragment of L dm1 . Finally, peptide maps of the D dm1 antigen show that the majority of its Arg peptides are identical to D d Arg peptides, whereas at least five of its Lys peptides and three of its Arg peptides correspond not to D d peptides but to L d and L dm1 peptides. These data raise the possibility that the D dm1 antigen is a hybrid molecule and they have also revealed an unexpected level of complexity in the dm1 mutant phenotype.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46737/1/251_2004_Article_BF00364331.pd

Functional and biochemical parameters of peptide antigen presentation

To understand the mechanism by which peptide antigens are processed and presented to T cells, we examined the T-cell response to the 13-amino-acid peptide [alpha]-melanocyte-stimulating hormone ([alpha]-MSH). To determine the fine specificity of T-cell recognition, T cells specific for [alpha]-MSH, and genetically restricted by I-Ab/d, were challenged with different [alpha]-MSH analogs and homologs. It was found that intact [alpha]-MSH, including the blocked amino and carboxy termini of the native molecule, was required for T-cell responsiveness. Antigen-presenting cells (APC) could be briefly pulsed with [alpha]-MSH and then present the [alpha]-MSH antigenic determinant to T cells, indicating that the relevant antigen was retained by the APC. APC stimulatory capacity was dramatically reduced by aldehyde treatment of the APC, or by pulsing the APC with [alpha]-MSH at low temperature. Efficient [alpha]-MSH pulsing was also impaired by treatment of the APC with the carboxylic ionophore, monensin, but not by the lysosomotropic agents chloroquine and methylamine. In addition, isolated APC plasma membranes added to the T cells in the presence of soluble [alpha]-MSH were not stimulatory. However, plasma membranes isolated from APC that had been previously pulsed with [alpha]-MSH retained stimulatory activity for T-cell responses. The only detectable [alpha]-MSH contained in these pulsed APC membranes was in an acid-stable complex of higher molecular weight than native peptide. The amount of [alpha]-MSH detected in the cellular membrane fraction isolated by density gradient sedimentation was also reduced by treatments that reduced the APC stimulatory capacity, such as pulsing at low temperature or in the presence of monensin. Taken together, these results suggest that processing of [alpha]-MSH is unlike that heretofore described for other peptide antigens and seems to involve APC handling to form the stimulatory moiety presented on the APC surface.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27319/1/0000341.pd

Immunology For Medical Students

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The Sydney AFF score : a simple tool to distinguish females presenting with atypical femur fractures versus typical femur fractures

Atypical femur fractures (AFF) are a rare but serious complication of long-term bisphosphonate use. Although clearly defined by ASBMR criteria, a proportion of patients with AFFs may go unrecognized and the use of qualitative fracture criteria may lead to uncertainty in AFF diagnosis, with significant therapeutic implications. A score that rapidly and accurately identifies AFFs among subtrochanteric femur fractures using quantitative, measurable parameters is needed. In a retrospective cohort of 110 female patients presenting with AFFs or typical femur fractures (TFFs), multiple logistic regression and decision tree analysis were used to develop the Sydney AFF score. This score, based on demographic and femoral geometry variables, uses three dichotomized independent predictors and adds one point for each: (age ≤80 years) + (femoral neck width <37 mm) + (lateral cortical width at lesser trochanter ≥5 mm), (score, 0 to 3). In an independent validation set of 53 female patients at a different centre in Sydney, a score ≥2 demonstrated 73.3% sensitivity and 69.6% specificity for AFF (area under the receiver-operating characteristic curve [AUC] 0.775, SE 0.063) and remained independently associated with AFF after adjustment for bisphosphonate use. The Sydney AFF score provides a quantitative means of flagging female patients with atraumatic femur fractures who have sustained an AFF as opposed to a TFF. This distinction has clear management implications and may augment current ASBMR diagnostic criteria