Human pulmonary surfactant protein A (SP-A) is encoded by two genes, SP-A1 and SP-A2. Reports from our laboratory and other investigations have shown heterogeneity in both genes within three regions (the 5' untranslated [5' UT], the coding, and the 3' untranslated [3' UT] regions). To more fully examine the variability in these regions and characterize the transcription start site in each gene, we used primer extension and 5' RACE to clone and then sequence cDNA clones from two individuals. These cDNAs extended from the transcription start site to approximately 40% of the 3' UT segment. The in vitro translatability of selected cDNAs was also tested. After analysis of our data, we found that: (1) the 5' UT of SP-A genes contains four (A, B, C, D for SP-A1) or three (A, B, D for SP-A2) untranslated exons, three of which (A, B, D) vary in length, and one of which (C) is new; (2) these exons are alternatively spliced and the major splice patterns as well as their relative frequency vary between the two genes (the major pattern for SP-A1 is AD'[81%] and the major patterns for SP-A2 are ABD [44%] and ABD'[49%]); (3) the SP-A1 gene uses three transcription start sites with equal frequency, whereas the SP-A2 gene uses only one; (4) splicing variability occurs among alleles and among individuals; (5) three previously undescribed alleles exist for the SP-A1 gene (6A2, 6A3, 6A4) and two for the SP-A2 gene (1A1, 1A2); and (6) a core group of 10 invariant nucleotides and four invariant amino acids can be used to discriminate between SP-A1 and SP-A2 alleles.

Severe infection causes marked derangements in the flow of glutamine among organs, and these changes are accompanied by significant alterations in regional cell membrane transport and intracellular glutamine metabolism. Skeletal muscle, the major repository of glutamine, exhibits a twofold increase in glutamine release during infection, which is associated with a significant increase in endogenous glutamine biosynthesis. Despite an increase in glutamine synthetase activity in skeletal muscle, the intracellular glutamine pool becomes depleted, indicating that release rates exceed rates of synthesis. Simultaneously, the circulating pool of glutamine does not increase, indicating accelerated uptake by other organs. The liver appears to be the major organ of glutamine uptake in severe infection; studies in endotoxemic rodents have shown net hepatic glutamine uptake to increase by as much as 8- to 10-fold. This increase is due partially to increases in liver blood flow, but also to a three- to fourfold increase in hepatocyte System N activity in the liver. Cytokines and glucocorticoids mediate the increased uptake of glutamine by the liver in septic states as well as other compounds. Sepsis does not appear to induce an increase in System N gene expression, indicating that the increase in hepatic glutamine transport observed during severe infection is probably regulated at the protein level. The bowel displays a decrease in glutamine utilization during sepsis, a response that may be related to the decrease in circulating insulin-like growth factor-1 (IGF-1) levels that is characteristic of sepsis. Recent studies suggest that IGF-1 has a direct effect on stimulating glutamine transport across the gut lumen and thus may represent a therapeutic avenue for improving gut nutrition during severe infection. The cells of the immune system (lymphocytes, macrophages) are also major glutamine consumers during inflammatory states in which cell proliferation is increased. Under these conditions, glutamine availability can become rate limiting for key cell functions, such as phagocytosis and antibody production.

Human pulmonary surfactant protein A (SP-A) is encoded by two genes, SP-A1 and SP-A2, that exhibit coding sequence (allelic) and 5´ splicing variability. In this report we determine the effect of the genetic variability within the SP-A1 and SP-A2 genes on the level of SP-A mRNAs and on the SP-A2 splicing variants in different individuals. We analysed mRNA specimens from 23 unrelated adults using genotype analysis, Northern analysis and primer extension, and made the following observations. (1) The level of SP-A mRNA varies among individuals (coefficient of variation = 0.49). One SP-A genotype (6A26A21A01A0) appears to be associated with a low to moderate level of SP-A mRNA. (2) The SP-A1/SP-A2 mRNA ratio varies among individuals, from 0.94 (lowest) to 6.80 (highest) within the study population. One genotype appears to be associated with a moderate to high SP-A1/SP-A2 mRNA ratio and another with a low to moderate ratio. (3) There is no correlation between the level of SP-A mRNA and the SP-A1/SP-A2 mRNA ratio. (4) Variability in the ratio of the major SP-A2 splice variants among individuals results from nucleotide differences in the splice-recognition sequence of specific SP-A2 alleles. The SP-A mRNA levels, the SP-A1/SP-A2 mRNA ratio, and the ratio of the major SP-A2 splice variants have a genetic basis in that they vary depending upon the specific SP-A alleles present.

Pulmonary surfactant, a lipoprotein complex, is essential for normal lung function, and deficiency of surfactant can result in respiratory-distress syndrome (RDS) in the prematurely born infant. Some studies have pointed towards a genetic contribution to the aetiology of RDS. Because the surfactant protein B (SP-B) is important for optimal surfactant function and because it is involved in the pathogenesis of pulmonary disease, we investigated the genetic variability of the SP-B gene in individuals with and without RDS. We identified a 2.5 kb BamHI polymorphism and studied its location, nature and frequency. We localized this polymorphism in the first half of intron 4 and found that it is derived by gain or loss in the number of copies of a motif that consists of two elements, a 20 bp conserved sequence and a variable number of CA dinucleotides. Variability in the number of motifs resulting from either deletion (in 55.3% of the cases with the variation) or insertion (44.7%) of motifs was observed in genomic DNAs from unrelated individuals. Analysis of 219 genomic DNAs from infants with (n = 82) and without (n = 137) RDS showed that this insertion/deletion appears with significantly higher frequency in the RDS population (29.3 as against 16.8%, P < 0.05).