The peptide-binding properties of the nonclassical major histocompatibility complex (MHC) class 1b molecule Qa-1 were investigated using a transfected hybrid molecule composed of the alpha 1 and alpha 2 domains of Qa-1b and the alpha 3 domain of H-2Db. This allowed the use of a monoclonal antibody directed against H-2Db whilst retaining the peptide-binding groove of Qa-1b. By comparison with classical MHC class I molecules, intracellular maturation of the chimeric molecule was inefficient with weak intracellular association with beta 2-microglobulin. However, at the cell surface the hybrid molecules were stably associated with beta 2-microglobulin and were recognized by cytotoxic T lymphocyte (CTL) clones specific for the Qa-1b-presented peptide Qdm (AMAPRTLLL). A whole-cell binding assay was used to determine which residues of Qdm were important for binding to Qa-1b and CTL clones served to identify residues important for T cell recognition. Substitutions at position 1 and 5 did not reduce the efficiency of binding and had little effect on CTL recognition. In contrast, substitutions at position 9 resulted in loss of MHC class I binding. Mass spectrometric analysis of peptides eluted from immunopurified Qa-1b/Db molecules indicated that Qdm was the dominant peptide. The closely related peptide, AMVPRTLLL, which is derived from the signal sequence of H-2Dk, was also present, although it was considerably less abundant. The mass profile suggested the presence of additional peptides the majority of which consisted of eight to ten amino acid residues. Finally, the finding that a peptide derived from Klebsiella pneumoniae can bind raises the possibility that this non-classical MHC class I molecule may play a role in the presentation of peptides of microorganisms.

NK cells acquire the ability to recognize MHC class I molecules during development. Studies with Qa‐1b tetramers (Qa‐1 tetramers) showed that nearly all NK1.1+ cells from newborn C57BL / 6 mice express Qa‐1‐binding receptors. Cytotoxic activity of these cells is fully inhibited by Qa‐1 ligands on target cells. In contrast, neither receptors for H‐2Kb nor H‐2Db were observed on NK1.1+ cells from newborn mice. After birth, frequencies of Qa‐1 tetramer+ / NK1.1+ cells gradually decrease as the number of Ly49+ / NK1.1+ cells increases. Cell transfer studies showed that Qa‐1 tetramer+ cells from newborn mice do not lose expression of Qa‐1 receptors, but that they further acquire expression of Ly49 molecules. Acquisition of Qa‐1‐binding receptors appears largely independent of host MHC class I molecules, as observed in studies using β2‐microglobulin‐deficient (β2m– / –) mice as well as Kb / Db – / – and Kb / Db / β2m– / – mice. The present results suggest that Qa‐1‐binding receptors play an important role in the specificity of developing NK cells, and suggest that these cells rely mainly on inhibitory receptors specific for non‐classical MHC class I molecules to maintain self tolerance during the first weeks of life.

An overview of a series of experiments attempting to link iron and calcium redistribution and release of free fatty acids with falls in pH and adenine nucleotide levels during cold storage of rabbit kidneys is presented. The data reviewed strongly suggest that these events are inextricably linked to subsequent reperfusion injury. Circumstantial evidence incriminating iron was provided by experiments showing that iron chelation decreased reperfusion injury after warm (WI) and cold ischaemia (CI) in rat skin flap and rabbit kidney models. Evidence for a role for calcium was provided when it was found that a calcium channel blocking agent added to the saline flush solution before storage inhibited lipid peroxidation, whereas chemicals which caused release or influx of calcium into the cell exacerbated oxidative damage. Additional involvement of breakdown products of adenine nucleotides was suggested by the protection from lipid peroxidation afforded by allopurinol. Involvement of calcium-activated phospholipase A2 was strongly suggested by increases in free fatty acids during cold storage and both this increase and lipid peroxidation were inhibited by addition of dibucaine to the storage solution.

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