Role of ligands in the activation of LFA-1.

Lymphocyte function-associated-antigen-1 (LFA-1) is able to bind selectively to its ligands intercellular adhesion molecules 1 and 3 (ICAM-1 and ICAM-3), suggesting that LFA-1 can exist in distinct ligand-specific binding states. In the case of ICAM-1, apart from ligand itself and the recently cloned molecule cytohesin-1, the natural physiological regulators of LFA-1-mediated binding to ICAM-1 are unknown. We have investigated the role of ligands (ICAM-1 and ICAM-3) in LFA-1 activation by using ICAM-blocking monoclonal antibodies and a fixation protocol for "freezing" LFA-1 on the surface of cells after prior exposure to ICAM-1 and ICAM-3. These studies not only confirm that LFA-1 exists in distinct ICAM-specific activation states, but also demonstrate that ICAM-1 plays a role in the activation of LFA-1 binding to ICAM-3.

The sheep CD1 gene family contains at least four CD1B homologues.

We identified four cDNA sequences encoding sheep homologues of the CD1 molecule. The sheep sequences were selected from lambdagt11 thymocyte cDNA libraries by hybridization with a human CD1C probe and a homologous sheep probe. The SCD1B-42 and SCD1A25 sequences encode complete CD1 molecules. The third sequence, SCD1B-52, which is closely related to SCD1B-42 and may be an allele, has the sequence encoding the alpha3 region precisely deleted. The fourth sequence, SCD1T10, is truncated at the 5' end. All four sequences are related to the human CD1B and domestic rabbit CD1B-like sequences at both nucleotide and amino acid level. Comparison of the derived CD1 amino acid sequences with the sequence of major histocompatibility complex class I molecules showed that the sheep CD1 molecules, like human CD1 molecules, lack most of the conserved class I residues known to be involved in interaction with beta2-microglobulin and the CD8 molecule. They do not contain the peptide docking residues involved in anchoring peptides in the peptide binding groove of class I molecules. Southern hybridization of sheep DNA with a sheep CD1 exon 4/alpha3 probe showed that the sheep genome encodes at least seven CD1 genes. The implications of these analyses for CD1 function are discussed.

Hepatitis C quantification and sequencing in blood products, haemophiliacs, and drug users.

The polymerase chain reaction (PCR) detected specific hepatitis C viral (HCV) RNA sequences in plasma from 15 of 21 haemophiliacs (12 HCV-antibody positive) and 7 of 27 intravenous drug users (13 HCV-antibody positive). Quantification of RNA-positive samples showed high levels of HCV (10(5) to 10(6) copies of RNA/ml) in infected patients. HCV was more frequently found in haemophiliacs infected with human immunodeficiency virus (11/11 HIV-positive and 4/10 HIV-negative patients). HCV-RNA was detected in all batches of commercially available factor VIII tested and in low concentrations in some pools of plasma donations from volunteers. Factor VIII, manufactured from volunteer donations, was uniformly negative by PCR. Phylogenetic analysis of viral sequences showed two distinct groups: one was associated with intravenous drug users and the other with haemophiliacs infected with Scottish factor VIII preparations. Both were distinct from sequences found in commercially available factor VIII.

The effect of motivation and word characteristics on recognition.

Two tachistoscopic studies assessed the effects of motivation on high-speed word processing. Study 1 assessed the effect of anxiety and Study 2 the effect of hunger compared to satiation. Words differed in interletter associative frequency (generated value), Thorndike-Lorge word frequency, and categories. In both studies, all three word variables yielded significant main effects. Motivational relevance of words did not significantly alter word recognition, the food words being most readily recognized and negatively emotional words least readily recognized in both studies. Anxiety did not have a significant effect, but hunger in interaction with word characteristics was found to be facilitating. Contrary to Hullian theory regarding word dominance and drive interaction and to Broadbent's "filtering" hypothesis, hunger in comparison to satiation increasingly facilitated word recognition the more infrequent the words and the more rare were the interletter associations.

The effect of food and water deprivation and satiation on recognition.

Food and water deprived and satiated subjects, as well as control subjects, were shown words presented tachistoscopically for .01 sec until word recognition. Five food-relevant, five water-relevant, and five neutral (animal) words of high string frequency were matched for letter confusability and letter predictability. Analyses of the data, in terms of number of presentations until recognition as well as number of words recognized at selected presentations, revealed that the amount but not the type of deprivation significantly altered word recognition. Moreover, the effect of motivation was significant already on the first slide presentation, while the effects of word characteristics (word category and generated value) occurred only after a number of presentations.