Was the evolutionary road towards adaptive immunity paved with endothelium?

Area of Science:

• Evolutionary immunology
• Comparative genomics
• Vertebrate physiology

Background:

• Jawless vertebrates possess a novel adaptive immune system (AIS), prompting questions about its duplicated evolution in vertebrates versus its absence in invertebrates.
• Existing theories for AIS evolution in vertebrates are challenged by causality issues and recent findings, necessitating a new perspective.

Purpose of the Study:

• To propose that evolutionary constraints in invertebrates, rather than selective pressures, prevented AIS development.
• To hypothesize that specific vertebrate vascular innovations facilitated the effective implementation of an AIS.

Main Methods:

• Phylogenetic analysis to determine if AIS preceded vascular innovations.
• Correlation analysis between vascular parameters and AIS investment.
• Modeling to assess the impact of vascular innovations on AIS efficacy.

Main Results:

• Vertebrate vascular innovations, including lower blood volume for higher antibody titers and enhanced circulatory dynamics for "epitope sampling," were crucial for AIS implementation.
• The proposed hypothesis suggests a strong link between physiological context and the evolution of complex immune systems.

Conclusions:

• The hypothesis explains the immunological differences between vertebrates and invertebrates.
• Immunity is influenced by factors beyond the immune system itself, highlighting the role of physiological context.