Larval T Cells Are Functionally Distinct from Adult T Cells in Xenopus laevis

Area of Science:

• Developmental immunology
• Comparative immunology
• Amphibian immunology

Background:

• The amphibian Xenopus laevis tadpole is a model for studying early immune development.
• Tadpoles primarily utilize innate-like T (iT) cells, unlike adult vertebrates dominated by conventional T cells.
• Understanding T cell ontogeny in tadpoles offers insights into early immune system evolution.

Purpose of the Study:

• To investigate the ontogenesis of T cell responsiveness in Xenopus laevis tadpoles and adult frogs.
• To compare T cell proliferation and activation in vivo and in vitro in tadpoles versus adults.
• To characterize the molecular signature of T cell responses during early development.

Main Methods:

• Assessed splenic T cell proliferation in vivo (pathogen infection) and in vitro (PHA stimulation) using 5-ethynyl-2 eal;-deoxyuridine and flow cytometry.
• Analyzed T cell activation and immediate-early gene expression via RT-quantitative PCR.
• Compared T cell signaling amplitude and kinetics between tadpole and adult splenocytes.

Main Results:

• Tadpole splenic T cells demonstrated limited in vivo proliferation but enhanced in vitro proliferation compared to adult T cells.
• Gene markers for T cell activation and immediate-early genes showed similar kinetics in both tadpoles and adults.
• Tadpole T cells exhibited a lower amplitude of T cell receptor (TCR) signaling, characteristic of innate-like or memory-like T cells.

Conclusions:

• Xenopus laevis tadpole T cells are functionally distinct from adult T cells.
• The tadpole T cell profile resembles mammalian neonatal T cells, suggesting conserved features of early immune development.
• These findings highlight the unique role of iT cells in early vertebrate immunity.