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The Tasmanian devil immune system studies

Chapter 4 – The science selected for study

4.3 The Tasmanian devil immune system studies

According to the Tasmanian devil scientific research literature no immune system studies of the Tasmanian devil had been undertaken prior to the detection of DFTD.

Richmond Loh in his initial research into the devil cancer found that devils with DFTD did not mount an immune response, stating ‘[i]n most DFTD tumours there is little evidence of a cell mediated immunological reaction with only 7% containing any evidence of lymphocyte infiltration’.11 Loh’s research found more than 95% of devils with DFTD were between the ages of 2 and 4 years, which he found puzzling, and he recommended immune system studies on devils with DFTD.12 Following Loh’s observations and recommendations two studies on the devil immune system were undertaken. The devil samples were provided by the DPIPWE from their own captive breeding program and the studies were funded by the DPIPWE. Associate Professor Greg Woods and his then PhD student Alex Kreiss of the Menzies Research Institute undertook studies at the Royal Hobart hospital laboratory to assess firstly, the devils’

immune structure and function and secondly, test for the possible development of a DFTD vaccine.

In 2008 Kreiss and colleagues concluded that the Tasmanian devils have a fully functioning immune system.13 This result in devils was contrary to findings in other studies on a range of marsupial species, which had indicated a poorly developed immune system.14 In concluding their article Kreiss et al ambiguously state:

11 Loh RC, 2006, The Pathology of Devil Facial Tumour Disease in Tasmanian Devils (Sarcophilus harrisii), Master of Philosophy, Murdoch University, Perth, Western Australia, p 90

12 ibid, p 94

13 Kreiss A, Fox N, Bergfeld J, Quinn SJ, Pyecroft S & Woods GM, 2008, Assessment of cellular immune responses of healthy and diseased Tasmanian devils (Sarcophilus harrisii), Developmental and Comparative Immunology, Vol. 32, pp 544-553

14 ibid, p 551

[t]here was no difference in immune responses between healthy and susceptible animals, but the need for high concentrations of mitogens may suggest that induction of immunity requires a strong stimulus. Importantly, susceptibility to DFTD is not a consequence of severely impaired cell-mediated immunity.

However, as the variation in responses was large one may hypothesise that devils undergo transient periods of immunosuppression, potentially during periods of high stress, such as during mating season, and at this stage could be more susceptible to DFTD.15

Further they state ‘[i]f immune suppression is an important contributing factor to the transmission of DFTD, it was not due to an inability to induce lymphocyte stimulation and proliferation’.16 This finding appears contrary to Loh’s finding of little evidence of lymphocyte infiltration in the DFTD tumours, as discussed on the previous page.

Kreiss et al did not undertake a study of devil macrophages because they claimed it was deemed that the extraction process of these cells would be too invasive.17 In a review of the book The Macrophage (2nd Ed.) published in the British Journal of Cancer in 2003, the reviewers state ‘macrophages are part of the innate immune system which allows organisms to distinguish between self and non-self as opposed to the adaptive immune system comprising B and T lymphocytes; in relation to cancer, macrophages form a significant proportion of the total cell population in a vast majority of tumour tissue’.18 A study of devil macrophages in relation to DFTD remains undone.

15 Kreiss A, Fox N, Bergfeld J, Quinn SJ, Pyecroft S & Woods GM, 2008, Assessment of cellular immune responses of healthy and diseased Tasmanian devils (Sarcophilus harrisii), Developmental and Comparative Immunology, Vol. 32, pp 544-553

16 ibid, p 552

17 ibid, p 552

18 Embleton MJ, 2003, Book Review, Burke, B & Lewis CE, 2002, The Macrophage (2nd Edn), Oxford University Press, Oxford, British Journal of Cancer, Vol 89, p 421

Kreiss and colleagues published the results of a second study of the devil immune system in 2009.19 This study was limited because of the lack of availability of a statistically significant number of devils due to restrictions under the Tasmanian Threatened Species legislation. A permit (TFA 08088) granted by the DPIPWE was however issued to take a restricted number of devils for scientific purposes.20 These devils included: 4 wild devils (roadkill); 2 captive devils; and a three-week old pouch young (mother died from DFTD). All were claimed to appear healthy and DFTD-free.

Notwithstanding the limited number of study specimens Kreiss et al concluded,

‘Tasmanian devil lymphoid tissues have all the structural elements required for effective T- and B-cell immune responses to disease.’21 However, this claim was qualified by the statement ‘[t]here were some minor variations between the samples studied (data not shown) because of the opportunistic nature of the sampling, but it was beyond the scope of this article to compare different animals.’22 They admitted ‘it is not yet clear why DFTD-affected devils fail to develop effective immunological rejection for the facial tumor allograft…’ but speculated that the ‘paucity of lymphocyte infiltration in association with tumors’ reported by Loh ‘may be explained by low MHC diversity in the devil populations where high prevalence of DFTD has been detected.’ 23 In this article the authors accept Loh’s observation and propose a new explanation for the lack of lymphocyte infiltration in the tumours. The evidence for the explanation, that low MHC diversity may be the cause of the lack of lymphocytes in the tumours, is in

19 Kreiss A, Obendorf DL, Hemsley S, Canfield PH & Woods GM, 2009, A Histological and

Immunohistochemical Analysis of Lymphoid Tissues of the Tasmanian Devil, The Anatomical Record:

Advances in Integrative Anatomy and Evolutionary Biology, Vol. 292(5), pp 611-620

20 ibid, p 612

21 Kreiss A, Obendorf DL, Hemsley S, Canfield PH & Woods GM, 2009, A Histological and

Immunohistochemical Analysis of Lymphoid Tissues of the Tasmanian Devil, The Anatomical Record:

Advances in Integrative Anatomy and Evolutionary Biology, Vol. 292(5), pp 611-620, pp 615-616

22 ibid, p 616

23 ibid, p 619

reference to an initial study published in 2007 by Siddle et al.24 The Siddle et al study published in October 2007 in PNAS makes the claim ‘DFTD is a transmissible tumor that spreads through a population due to a lack of histocompatibility barriers.’25 This hypothesis, that a lack of histocompability barriers was the reason for transmissibility of the devil cancer, was later proven false.

At the time, however, this hypothesis formed the basis for further studies to determine if the Tasmanian devil immune system had the ability to recognise foreign cells. This study, published in 2009, was undertaken by Kreiss, Wells and Woods and tested antibody responses in devils over 40 weeks.26 These experiments were undertaken in both in vitro27 and in vivo28 to evaluate the humoral immune response29 of the Tasmanian devil. Again it was also noted that due to the endangered status of the devils only four devils, all of which were maintained by DPIPWE, were used in the experiments. Their findings indicated that Tasmanian devils are able to mount a humoral immune response as well as a memory response following two types of injections. However, cytotoxic T lymphocytes responses were not evaluated. According

24 Kreiss A, Obendorf DL, Hemsley S, Canfield PH & Woods GM, 2009, A Histological and

Immunohistochemical Analysis of Lymphoid Tissues of the Tasmanian Devil, The Anatomical Record:

Advances in Integrative Anatomy and Evolutionary Biology, Vol. 292(5), pp 611-620

25 Siddle, HV, Kreiss A, Eldridge MDB, Noonan, E, Clarke, CJ, Pyecroft, S, Woods GM & Belov K, 2007, Transmission of a fatal clonal tumor by biting occurs due to depleted MHC diversity in a threatened carnivorous marsupial, PNAS, Vol 104(41), 16221-16226, p 16224, p 16225

26 Kreiss A, Wells B & Woods GM, 2009, The humoral immune response of the Tasmanian devil (Sarcophilus harrisii) against horse red blood cells, Veterinary Immunology and Immunopathology, Vol 130, pp 135-137

27 In vitro: literally in glass; as in a test tube. Available at:

http://www.medterms.com/script/main/art.asp?articlekey=4033 last accessed 17 August 2010

28 In vivo: in the living organism, as opposed to in vitro (in the laboratory). Available at:

http://www.medterms.com/script/main/art.asp?articlekey=4034 last accessed 17 August 2010

29 Humoral refers to the non-cellular components of the blood, such as plasma and lymphatic fluid. The humoral immune response denotes immunologic responses that are mediated by antibodies. Available at:

http://www.uptodate.com/contents/the-humoral-immune-response last accessed 30 December 2012

to Ito and Seishima ‘[c]ytotoxic T lymphocytes (CTLs)30 constitute a distinct lymphocyte sub-population, and are induced by several diverse stimuli including major histocompatibility antigens... CTLs are involved in adaptive immune responses and are key players in mediating immunity against pathogens and tumors.’31 Kreiss et al were aware that ‘a successful anti-DFTD vaccine should also induce cytotoxic T cell activity, as this is the traditional immune response against tumours’.32 It would appear that again this study lacked sufficient devil numbers to provide statistically significant results and critical studies were left undone.

Despite the inconclusive nature of the findings of the Tasmanian devil immune system studies, DFTD researchers continue to claim that the devils’ immune system is not compromised. In order to demonstrate that immune competence is an anomaly in the Tasmanian devil malignant cancer, a comparison is given in the next section between four wildlife species, including the Tasmanian devil, threatened with extinction from cancer.