An analysis of afferent lymph dendritic cells during cutaneous chemical carcinogenesis
Creators: name: Ragg, Scott J
Publisher: name: University Of Tasmania
Year: 2023

description: To investigate the mechanism(s) of carcinogen-induced alterations to epidermal LC density and function, sheep pseudoafferent lymphatic vessels draining a defined area of skin were cannulated thereby allowing direct sampling and enumeration of LC migration. Topical application of the complete carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) caused a biphasic increase in the rate of LC migration, the second peak representing in excess of a 100-fold increase in LC migration. Benzo[a]pyrene (BP), a complete carcinogen, also caused an immediate 2-4 fold increase in the rate of LC migration which was sustained for the duration of the experiment. The tumour promoter TPA caused an immediate 2-4 fold increase in the rate of LC migration while the tumour initiator urethane did not alter LC migration. These experiments demonstrated that the changes in epidermal LC density and distribution observed after topical application of chemical carcinogens are due to altered LC migration and are not a consequence of chemical toxicity or cell death. Since dendritic cells (DC), which include the LC, continue to migrate from the carcinogen-treated skin despite a reduction in cutaneous immune status, the functional capacity of these migrating DC required analysis. The complete carcinogens DMBA and BP both caused long term abrogations in the antigen-presenting capacity of migrating DC. In contrast, the tumour promoter TPA reduced DC function for less than 1 week after a single topical application. Bilateral cannulation of prefemoral afferent lymphatic vessels determined that these reductions in DC function were entirely attributable to the carcinogen. These studies demonstrated that chemical carcinogens cause a long term abrogation of epidermal DC function resulting in reduced cutaneous immunity. To examine the possibility that altered cytokine secretion by carcinogen-treated DC may play a role in the depletion of antigen-presenting function, DC:T cell co-cultures were set up in parallel to the antigen presentation assays. Supernatants were assayed for the presence of the DC-derived cytokines IL-11˜í‚â§, TNF-˜í¬±, prostaglandin E2 and interferon-y. While present in normal co-cultures, IL-11˜í‚â§ was absent from cultures involving carcinogen-treated DC indicating that a crucial costimulatory signal is absent from these cultures. The immunosuppressive factor PGE2 was detected in cultures derived from BP-treated DC. The experiments performed in this thesis have further defined the role of DC/LC during the early stages of chemical carcinogenesis, in particular the alteration of their normal migration patterns from the skin to the regional lymph node and the concurrent abrogation of antigen-presenting function. The results clearly demonstrate that epidermal DC are functionally depleted during chemically-induced tumour development and provide further evidence in support of the hypothesis that impaired immunosurveillance by epidermal antigen-presenting cells will increase the probability of tumour development.