11 Jan Appendix May Play An Important Role As a Secondary Immune Organ

MedicalResearch.com Interview with:
Heather F. Smith, Ph.D.
Associate Professor of Anatomy
Midwestern University
Glendale, AZ 85308

MedicalResearch.com: What is the background for this study?

Response: The appendix is a narrow pouch that projects off the cecum in the digestive system of many mammal species. Between 1-6% of humans will suffer from appendicitis (inflammation of the appendix) at some point in their lives. Although it is widely viewed as a vestigial organ with little known function, recent research suggests that the appendix may serve an important purpose. My research team gathered data on the presence or absence of the appendix and other gastrointestinal and environmental traits for 533 mammal species. We mapped the data onto a phylogeny (genetic tree) to track how the appendix has evolved through mammalian evolution, and to try to determine why some species have an appendix while others don’t.

MedicalResearch.com: What are the main findings?

Response: We discovered that the appendix has evolved independently in several mammal lineages, over 30 separate times, and almost never disappears from a lineage once it has appeared. This suggests that the appendix likely serves an adaptive purpose. Looking at ecological factors, such as diet, climate, how social a species is, and where it lives, we were able to reject several previously proposed hypotheses that have attempted to link the appendix to dietary or environmental factors. Instead, we found that species with an appendix have higher average concentrations of lymphoid (immune) tissue in the cecum. This finding suggests that the appendix may play an important role as a secondary immune organ. Lymphatic tissue can also stimulate growth of some types of beneficial gut bacteria, providing further evidence that the appendix may serve as a “safe house” for helpful gut bacteria.

MedicalResearch.com: What should readers take away from your report?

Response: Multiple recent research studies now suggest that the appendix serves an adaptive function, and is not simply a vestigial organ. In particular, it serves to stimulate the immune system in response to pathogens, and serve as a “safe-house” for beneficial gut microflora (bacteria). While individuals who have had their appendix surgically removed, generally do not experience any major detrimental effects, some studies have found that they may experience higher rates of infection than individuals with an appendix.

MedicalResearch.com: What recommendations do you have for future research as a result of this study?

Response: My research team is now expanding this study to look at the counterpart of the appendix in birds, which are called the colic ceca. We are assessing whether the colic ceca in birds may serve the same function(s) as the appendix in mammals, or whether colic ceca also have a digestive function in some species, and what role dietary preferences may play in that relationship.  

MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.

Citation:

Heather F. Smith, William Parker, Sanet H. Kotzé, Michel Laurin. Morphological evolution of the mammalian cecum and cecal appendix. Comptes Rendus Palevol, 2017; 16 (1): 39 DOI: 10.1016/j.crpv.2016.06.001

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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Last Updated on January 11, 2017 by Marie Benz MD FAAD