Schistosoma mansoni: larval damage and role of effector cell(s) in the synergy between vaccine immunity and praziquantel treatment.

A number of authors have demonstrated that the schistosomicidal compound, Praziquantel (Pzq), depends for its action upon the immune status of the host (Sabah et al. 1985; Brindley & Sher, 1987; Doenhoff et al. 1987). We have attempted to define the synergistic interaction between immuno- and chemotherapy further, using the murine irradiated vaccine model of schistosomiasis mansoni. In vaccinated mice, resistance operates in the skin but not the lungs; drug targeted towards lung-stage worms exacerbates lung-phase immunity, however, as depicted by the increased number and size of inflammatory reactions in the pulmonary tissues. Parasites are often found trapped within such foci. In the present investigation, light and ultrastructural studies have been utilized to examine the nature and extent of damage inflicted upon lung-stage larvae recovered from day 6 Pzq-treated vaccinated mice. Such studies have revealed that damage involves muscle disorganization, internal disruption and occasionally, loss of the tegument; in the latter case, cells are often seen attached to the denuded lung worms. To identify the crucial cellular effector cell(s) involved in the synergy between immuno- and chemotherapy, cell depletion studies have been performed in vivo. It would appear from these experiments that eosinophils or lymphocytes rather than neutrophils or macrophages are important effector cells in this synergy. Histological studies argue in favour of eosinophils being the key effector cells.

The transcriptional control proteins c-Myb and v-Myb contain a basic region DNA binding motif.

A class of transcriptional control proteins, typified by c-Myb, are characterised by a highly conserved N-terminal DNA binding domain, which is composed of either 2 or 3 imperfect repeats of about 52 amino acids. A sequence homology search of the SWISSPROT protein sequence data bank with this region from mouse c-Myb has allowed us to identify an area near the C-terminus of repeat 2 that contains a short sequence motif, known as the basic region, which forms the DNA binding site in both leucine zipper and helix-loop-helix transcription factors. We therefore propose that this region of repeat 2 and the homologous part of repeat 3 will form the Myb DNA binding site.

Tests for the statistical significance of protein sequence similarities in data-bank searches.

A suite of tests to evaluate the statistical significance of protein sequence similarities is developed for use in data bank searches. The tests are based on the Wilbur-Lipman word-search algorithm, and take into account the sequence lengths and compositions, and optionally the weighting of amino acid matches. The method is extended to allow for the existence of a sequence insertion/deletion within the region of similarity. The accuracy of statistical distributions underlying the tests is validated using randomly generated sequences and real sequences selected at random from the data banks. A computer program to perform the tests is briefly described.

STATSEARCH: a GCG-compatible program for assessing statistical significance during DNA and protein databank searches.

We describe a program STATSEARCH which implements the method of Mott et al. (1989) for searching DNA and protein sequence databanks for statistically significant similarities to a given query sequence. STATSEARCH is written to run in conjunction with the GCG sequence analysis package.

Schistosoma mansoni: histological analysis of the synergistic interaction between vaccine immunity and praziquantel therapy in the lungs of mice.

Naive CBA mice and mice vaccinated 4 weeks previously with gamma-irradiated cercariae of S. mansoni were challenged percutaneously with normal cercariae and then treated with 500 mg/kg body weight of Praziquantel (Pzq). The drug was administered intradermally on day 1 or intramuscularly on day 6, thus targeting against skin stage or lung stage challenge larvae respectively. The skin site of challenge and/or the lungs were removed at various time points to provide samples for histological examination. As reported elsewhere (Flisser, Delgado & McLaren 1989) the efficacy of Pzq was significantly enhanced in vaccinated mice and was influenced by the treatment regime. Histological analysis revealed that when Pzq was administered I/D on day 1 to vaccinated mice, the inflammatory response to challenge differed in extent but not nature from that seen in vaccinated but untreated cohorts. This correlates with worm recovery data showing no (this study), or only marginal synergy between drug treatment and immunity using this regimen of drug treatment (Flisser et al. 1989). Following the day 6 protocol of drug delivery, however, lungs from treated vaccinated mice exhibited many large inflammatory reactions containing trapped challenge larvae. In contrast, lungs from untreated vaccinated mice had only few foci which were small and rarely contained trapped larvae. These data again correlate well with worm recovery data showing that there is a highly significant synergy between vaccination and drug treatment administered at this time (Flisser et al. 1989; this study). It would seem, therefore, that Pzq exacerbates lung phase immunity in the NIMR vaccine mouse model where skin phase immunity predominates and pulmonary attrition is normally minimal. The results are discussed in the light of published data concerning the effector mechanisms thought to characterize skin and lung phase vaccine resistance in the murine model.

An accurate approximation to the distribution of the length of the longest matching word between two random DNA sequences.

An accurate approximation is derived to the distribution of the length of the longest matching word present between two random DNA sequences of finite length, using only elementary probability arguments. The distribution is shown to be consistent with previous asymptotic results for the mean and variance of longest common words. The application of the distribution to assessing the statistical significance of sequence similarities is considered. It is shown how the distribution can be modified to take account of non-independence of neighbouring bases in real sequences.

A test for the statistical significance of DNA sequence similarities for application in databank searches.

A method is developed, based on word-searching, which provides a rapid test for the statistical significance of DNA sequence similarities for use in databank searching. The method makes allowance for the lengths and dinucleotide compositions of the sequences being compared. A way is also described to calculate the power of the test, i.e. the probability of detecting a given similarity as being statistically significant. The effects on the power of the test of the scoring method, word length, sequence length, and sequence composition are examined. A novel scoring method is shown to be superior to the method currently used in most word-searching algorithms.