Effects of Stress Conditions on the Immune System of Caiman latirostris

ANA PAULA MESTRE; JULIETA VERÓNICA CARLETTI; MARÍA SOLEDAD MOLEÓN; PATRICIA SUSANA AMAVET; PABLO ARIEL SIROSKI

Santa fe

Congreso; 25th Working Meeting of the IUCN-SSC Crocodile Specialist Group; 2018

IUCN-SSC Crocodile Specialist Group

The immune system (IS) is essential in the animals to monitor the ability to defend from infections, health status, and different changes in the external environment. Some stressors, especially hormonal factors, can affect this system. To test the effects of stress conditions on the IS of Broad-snouted caiman (C. latirostris), we elevated corticosterone level by either restraining animals or additionally injecting pituitary adrenocorticotrophic hormone (ACTH) and compared their phytohemagglutinin (PHA) swelling response. Besides, we determinated the effects of these stressors on the others immunological parameters as differential white blood cell count (DWBC) and natural antibodies levels (NAb) titers. We compared all the immunological parameters 12, 24, 36 and 48 h after the immune challenge among three groups of caimans: (i) animals under restraint stress (n = 4), (ii) ACTH-injected animals (n = 4), and (iii) free-living animals-control- (n = 4). The results showed differences in PHA swelling response along the time but not among treatments, indicating a response independent of corticosterone levels. Nevertheless, it is interesting to note, that to respect to others authors, which found the higher response at 24 h after PHA inject, we found a late swelling response at 36 h. On the other hand, we found differences in DWBC count, where basophils population showed an increase in animals under restraint stress (i) respect to the control; suggest that this treatment can causing inflammatory bodily reactions, due to the increase of this type of leukocyte. Besides, the result revealed an increased only in control animals of their NAb titers over time (at 48 h), moment where the adaptive response begins to unchain, indicating the possible inhibition in the immune response in animals treated. Finally, the corticosterone levels showed differences among treatments but only along the time, where free-living animals-control-(iii) as well as animals under restraint stress (i) continued to increase their corticosterone levels over time, while the ACTH-injected animals (ii) reduced those levels at 48 h. This continuous increment of corticosterone levels in (i) and (iii) could be the result of the stress caused by animals in captivity; nevertheless, the reduction observed in (ii) could be indicating an antagonist effect of the ACTH injection on this hormone over time. The result of this preliminary study allow broadening the knowledge about endocrine and immune effects caused by stress conditions, but this need to be continued. Nevertheless, overall, these results provide evidence of a late PHA swelling response, as well as being suggest that stress conditions in C. latirostris could leading to structural and functional changes to immune system could result in a reduction of resistance of the host.