Lipopolysaccharide-induced CXC chemokine (LIX) is a novel murine neutrophil-chemoattractant CXC chemokine cloned as a glucocorticoidattenuated response gene. We investigated LIX message expression in an acute endotoxemia model. LIX message peaks later than KC or macrophage inflammatory protein-2 (MIP-2) and remains elevated longer in almost all tissues. Induced LIX message expression in heart is 5-to 6-fold greater than in lung and spleen, and 20-fold greater than in liver. In contrast, KC expression is equal in heart, lung, and liver, whereas MIP-2 expression is strongest in the lung. Glucocorticoid regulation of these genes also differs. Endotoxemia-induced LIX message expression in the lung is markedly enhanced in adrenalectomized mice and strongly attenuated by dexamethasone, whereas lung KC and MIP-2 expression are unaffected by glucocorticoids. It is surprising to note that endotoxemia-induced brain expression of LIX (but not KC or MIP-2) is increased by dexamethasone. These observations suggest that LIX may have biological roles distinct from KC and MIP-2. J. Leukoc. Biol. 64: 494-502; 1998.

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The murine CXC chemokine LIX has distinctive sequence features that suggest it is a novel chemokine. Among known human chemokines, ENA-78 and GCP-2 are the two most closely related to LIX. We have recently cloned the human GCP-2 gene. Phylogenetic analysis shows that the LIX coding region is more distant from both human GCP-2 and ENA-78 than is porcine AMCF-II, the chemokine with greatest sequence similarity to LIX. Human GCP-2 and ENA-78 have very high nucleotide similarity in non-coding as well as coding sequences, which suggests that these genes are the result of an evolutionarily recent gene duplication event. If this duplication occurred during primate evolution, then non-primate species may have only a single chemokine corresponding to this pair of human genes. This example shows that a one-to-one genetic correspondence does not necessarily exist between all the chemokine genes in two different species. These observations may have important implications for other chemokines that belong to clusters of closely related genes.

A comparative study of catalytic properties of the sperm-specific lactate dehydrogenase (EC 1.1.1.27) isozyme X or C4 from a variety of animals (boar, bull, goat, Guinea pig, man, mouse, pigeon, rabbit, and rat) is presented. Optimum concentration and Km values for pyruvate, inhibition by substrate, and activity against analog substrates (alpha-ketoacids with linear and branched chains from 4 to 6 carbon atoms) for isozyme X of different species showed significant differences. The observed properties are correlated with available evidence on the metabolic role of the enzyme.

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