Was the evolutionary road towards adaptive immunity paved with endothelium
Date
2015-09-04
Authors
Van Niekerk, Gustav
Davis, Tanja
Engelbrecht, Anna-Mart
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: The characterization of a completely novel adaptive immune system (AIS) in jawless vertebrates
(hagfish and lampreys) presents an excellent opportunity for exploring similarities and differences in design
principles. It also highlights a somewhat neglected question: Why did vertebrates, representing only 5 % of all
animals, evolve a system as complex as an AIS twice, whereas invertebrates failed to do so? A number of theories
have been presented in answer to this question. However, these theories either fail to explain why invertebrates
would not similarly develop an AIS and are confounded by issues of causality, or have been challenged by more
recent findings.
Presentation of the hypothesis: Instead of identifying a selective pressure that would drive the development of
an AIS, we hypothesise that invertebrates failed to develop an AIS because of the evolutionary constraints imposed
by these animals’ physiological context. In particular, we argue that a number of vascular innovations in vertebrates
allowed the effective implementation of an AIS. A lower blood volume allowed for a higher antibody titer (i.e., less
‘diluted’ antibody concentration), rendering these immune effectors more cost-effective. In addition, both a high
circulatory velocity and the ability of endothelium to coordinate immune cell trafficking promote ‘epitope
sampling’. Collectively, these innovations allowed the effective implementation of AIS in vertebrates.
Testing the hypothesis: The hypothesis posits that a number of innovations to the vascular system provided the
release from constraints which allowed the implementation of an AIS. However, this hypothesis would be refuted
by phylogenetic analysis demonstrating that the AIS preceded these vascular innovations. The hypothesis also
suggests that vascular performance would have an impact on the efficacy of an AIS, thus predicting a correlation
between the vascular parameters of a species and its relative investment in AIS. The contribution of certain vascular
innovations in augmenting immune functionality of an AIS can be tested by modelling the effect of different
vascular parameters on AIS efficacy.
Implications of the hypothesis: The hypothesis not only explains the immunological dimorphism between
vertebrates and invertebrates but also brings to attention the fact that immunity is dependent on more than just
an immune system.
Description
CITATION: Van Niekerk, G., Davis, T., & Engelbrecht, A-M. 2015. Was the evolutionary road towards
adaptive immunity paved with endothelium?. Biology Direct, 10:47, doi:10.1186/s13062-015-0079-0.
The original publication is available at http://www.biologydirect.com/content/10/1/47
Publication of this article was funded by the Stellenbosch University Open Access Fund.
The original publication is available at http://www.biologydirect.com/content/10/1/47
Publication of this article was funded by the Stellenbosch University Open Access Fund.
Keywords
Adaptive immune system, Evolutionary constraint, Endothelium, Inflammation, Vertebrate, Invertebrate
Citation
Van Niekerk, G., Davis, T., & Engelbrecht, A-M. 2015. Was the evolutionary road towards
adaptive immunity paved with endothelium?. Biology Direct, 10:47, doi:10.1186/s13062-015-0079-0.