No abstract

Clonal hematopoiesis is frequently observed in elderly people. To investigate the prevalence and dynamics of genetic alterations among healthy elderly individuals, a cohort of 50 people >80 years was genotyped for commonly mutated leukemia-associated genes by targeted deep next-generation sequencing. A total of 16 somatic mutations were identified in 13/50 (26%) individuals. Mutations occurred at low variant allele frequencies (median 11.7%) and remained virtually stable over 3 years without development of hematologic malignancies in affected individuals. With DNMT3A mutations most frequently detected, another cohort of 160 healthy people spanning all age groups was sequenced specifically for DNMT3A revealing an overall mutation rate of 6.2% (13/210) and an age-dependent increase of mutation prevalence. A significant difference (p = 0.017) in the DNMT3A expression pattern was detected between younger and healthy elderly people as determined by qRT-PCR. To evaluate the selection of clonal hematopoietic stem cells (HSCs), bone marrow of two healthy individuals with mutant DNMT3A was transplanted in a humanized mouse model. Xenografts displayed stable kinetics of DNMT3A mutations over 8 months. These findings indicate that the appearance of low-level clones with leukemia-associated mutations is a common age-associated phenomenon, but insufficient to initiate clonal selection and expansion without the additional influence of other factors.

1. The behaviour and development of Brugia patei has been followed in the mosquito host, Mansonia uniformis, from ingestion of the microfilariae to the development of the infective stages.2. The microfilariae penetrated very rapidly out of the stomach into the abdomen of the mosquito; 80% of them escape from the stomach during the first 50 minutes after a blood meal.3. The microfilariae migrate from the abdomen to the thorax through fat body cells and the heart during the first 140 minutes followed engorgement and begin to penetrate the indirect flight muscles within 15 minutes from engorgement. During this migration microfilariae were found in close association, suggesting that they follow similar pathways of migration through the body of the mosquito.4. Most microfilariae (98%) have settled in the indirect flight muscles within 2 hours of engorgement. In these muscles the larvae digest away the muscle surrounding them but do not begin to elongate until the third or fourth day after the blood meal. The rate of development varies from one mosquito host to another, but about 80% of the larvae have developed to the infective stage by the ninth to tenth days after the infective feed. The infective stages concentrate in the head and proboscis of the mosquito vector. The development of B. patei is faster than that of B. pahangi in mosquitoes from the same colony.5. The efficiency of M. uniformis as a vector of B. patei is compared with the similar efficiency of M. longipalpis as a vector of B. malayi. In both mosquitoes the majority of the microfilariae ingested develop to the infective stage. M. uniforms is also an efficient vector of B. pahangi.6. The development of the parasite is discussed briefly with reference to knowledge of the physiological events within the mosquito host subsequent to the blood meal.

1. The filarial worm Brugia patei was brought to London from East Africa in the larval stage developing in Mansonia mosquitoes. Subsequent transmission to domestic cats was possible in London through a laboratory colony of Mansonia uniformis and the worm was very infective to this species of mosquito. The worm was much less infective to Aedes togoi and Anopheles gambiae.2. Subsequent passage of the worm through Aedes togoi has increased its infectivity to this species of mosquito. The infection rate has risen from 43·6% in females of A. togoi fed on the cat original- ly infected by larvae from Mansonia mosquitoes, to 59·2% in females fed on a cat containing the first generation of worms to pass through A. togoi, to 79·1% in females fed on cats containing the second generation of worms to pass through A. togoi, to 86·7% in females fed on cats containing the third generation of worms to pass through A. togoi, to 89·8% in females fed on cats containing the fourth generation of worms to pass through A. togoi.3. The distributions of infective stage larvae in female mosquitoes were negative binomial distributions. These were related to the distributions of microfilarial intake immediately after infection which were also negative binomial. From one generation of worms passed through the new mosquito host to the next the mean and the k value of the negative binomial of the infective stage larvae approached the same parameters for the distribution of microfilarial intake. By the fourth generation of worms passed through A. togoi the distributions of microfilarial intake and infective stage larvae developing in A. togoi were similar, suggesting close adaptation to the new mosquito host. A similar relation between these distributions was found originally in Mansonia. There were however considerable differences in these distributions between the two species of mosquito.4. The experiment extended over a period of 6 years. The change in infectivity did not appear to be related to the microfilarial density, age of infection, or sex, in the mammalian host. Neither could it be related to the genetics of susceptibility in the mosquito, nor to mosquito culture techniques, nor to mosquito mortality.5. It is concluded that the observed change in infectivity is best explained by a change in adaptation of the worm to the new intermediate host by selection within the mosquito of those microfilariae adapted to it. No major change in infectivity to the original intermediate host, Mansonia, was found during the experiment.6. These findings are examined with reference to changes in adaptation to mosquito hosts in the history of Bancroftian filariasis.