Pneumocystis carinii causes a distinctive interstitial pneumonia in immunocompetent laboratory rats that had been attributed to "rat respiratory virus"

A prevalent and distinctive infectious interstitial pneumonia (IIP) of immunocompetent laboratory rats was suspected to be caused by a putative virus, termed rat respiratory virus, but this was never substantiated. To study this disease, 2 isolators were independently populated with rats from colonies with endemic disease, which was perpetuated by the regular addition of naive rats. After Pneumocystis was demonstrated by histopathology and polymerase chain reaction (PCR) in the lungs of rats from both isolators and an earlier bedding transmission study, the relationship between Pneumocystis and IIP was explored further by analyzing specimens from 3 contact transmission experiments, diagnostic submissions, and barrier room breeding colonies, including 1 with and 49 without IIP. Quantitative (q) PCR and immunofluorescence assay only detected Pneumocystis infection and serum antibodies in rats from experiments or colonies in which IIP was diagnosed by histopathology. In immunocompetent hosts, the Pneumocystis concentration in lungs corresponded to the severity and prevalence of IIP; seroconversion occurred when IIP developed and was followed by the concurrent clearance of Pneumocystis from lungs and resolution of disease. Experimentally infected immunodeficient RNU rats, by contrast, did not seroconvert to Pneumocystis or recover from infection. qPCR found Pneumocystis at significantly higher concentrations and much more often in lungs than in bronchial and nasal washes and failed to detect Pneumocystis in oral swabs. The sequences of a mitochondrial ribosomal large-subunit gene region for Pneumocystis from 11 distinct IIP sources were all identical to that of P. carinii. These data provide substantial evidence that P. carinii causes IIP in immunocompetent rats.

A cDNA from the green alga Spermatozopsis similis encodes a protein with homology to the newly discovered Roadblock/LC7 family of dynein-associated proteins

A clone, designated as B15, was isolated from a cDNA library of the unicellular green alga Spermatozopsis similis and characterised. The deduced amino acid sequence of its open reading frame exhibits high homology to members of the recently discovered roadblock/LC7 protein family (robl/LC7) of dynein-associated proteins. Homologies were highest to a robl/LC7-member from human testis (86%, identity 56%) and to the roadblock protein of Drosophila (88%, identity 52%). Data bank analyses revealed no homologies to known higher plant proteins. B15 is a single copy gene in the genome of Sperm-latozopsis and its transcript was detectable throughout the cell cycle.