Boosting the immune defense: Interleukin-2 promotes fate decisions in
CD8 T cells for long- or short-term immune protection

Date:
February 11, 2022
Source:
University of Alabama at Birmingham
Summary:
A new study shows how two subsets of one type of immune cell --
the CD8 T cell -- develop to provide either short-term or long-term
immune protection. The study focuses on one factor that guides
that developmental bifurcation -- interleukin-2, or IL-2.



FULL STORY ==========================================================================
The immune system is a complex network of cells and proteins with a
simple job.

Defend the body against infection. To do that, the cells must recognize
and destroy infecting viruses or bacteria. In addition, the system also
has to keep a record of each pathogen it has defeated, so it can quickly remobilize if infected again.


==========================================================================
A study in the journal Science Immunology now shows how two subsets of
one type of immune cell -- the CD8 T cell -- develop to provide either short-term or long-term immune protection. The study focuses on one factor
that guides that developmental bifurcation -- interleukin-2, or IL-2.

Understanding details of how nai"ve immune cells develop into effective infection-fighters or long-lived memory cells is important because it
can help us understand which constituents of a complex response are
necessary to provide protection against infections or cancers. It can
also aid understanding of immune system dysfunction, or it can improve immunotherapy for cancer.

Dysfunctions include autoimmune diseases, where the immune system
attacks the body's own cells, and exhaustion, where the immune system
loses its ability to fight off continuing infection or the ability to
destroy a cancer.

Study senior author Allan Zajac, Ph.D., and co-first authors Shannon
M. Kahan, Ph.D., and Rakesh K. Bakshi, Ph.D., all of the University of
Alabama at Birmingham Department of Microbiology, used mouse models to
follow the traits and fates of the two subsets of CD8 T cells, starting
from the peak of their effector phase, eight days after an acute viral infection.

CD8 T cells are a type of white blood cell that has the ability to
develop into effector T cells -- also known as cytotoxic T cells or
killer T cells. These cells can destroy cancer cells or cells infected
with viruses or bacteria. IL- 2 is a cytokine, one of a large family of
small signaling proteins that are released by cells to send messages to
other cells, or act as an autocrine signal to the same cell that is making
the cytokine. Cells receive the signal at the cell surface, where the
cytokine binds to a receptor. The receptor transduces the signal to the
cell interior, leading to changes in cell gene expression and phenotype.

Zajac and UAB colleagues were able to isolate and purify CD8 T cells
from mice at the effector phase peak. Using fluorescence-activated cell
sorting after cell stimulation with a viral antigen, they identified
two subsets of this group -- a minority of the CD8 T cells that produced
IL-2 and a majority that did not produce IL-2.



==========================================================================
The two subsets turn out to be strikingly different in the short term, in
terms of developmental transitions that lead to fate decisions. However,
they then become more alike months later.

The cells that produced IL-2 developed like immune memory
cells. They attained stem-like memory traits, resisted exhaustion and preferentially conferred protective immunity upon a secondary viral
challenge. Counterintuitively, they did not respond to their own IL-2,
which acts inside the cell through a complex called STAT5, or signal
transducer and activator of transcription. Even though the IL-2-producing
CD8 T cells had normal amounts of IL-2 receptor proteins on the cell
surface, the level of phosphorylated-STAT5 inside the cell -- which is
the activated form of STAT5 -- was greatly diminished. The researchers hypothesized several mechanisms acting inside the cell possibly acting
to attenuate the ability to receive IL-2-dependent STAT5 signals, but
the answer is not yet known.

In contrast to the IL-2-producing cells, the non-IL-2-producing effector
cells did respond to IL-2 signals, and they then gained effector traits
at the expense of memory formation.

The UAB researchers did RNA sequencing of the cell subsets during the
effector phase, nine days after infection, and much later, during the
memory phase, about 10 months after infection. The transcriptional
profiles of the IL-2- producing and the IL-2-non-producing effector
populations were unique and distinguishable from their memory
counterparts. However, by the memory time point, the two populations
were more related to each other in gene expression.

Thus, despite having distinct properties during the effector phase,
the IL-2- producing and ?nonproducing CD8 T cells appeared to converge
as memory matured to form populations with equal recall abilities to
respond to a second viral infection or chronic viral challenge.

"This bifurcation between the ability of IL-2-producing and -nonproducing
CD8 T cells to respond to IL-2 couples functional competency with fate decisions, and it implicates IL-2 as a critical differentiation factor,"
Zajac said. Zajac notes that the salient findings of this study have not
yet been confirmed for humans, and they are restricted to analyzing CD8
T cell responses to a single pathogen.

Co-authors with Zajac, Kahan and Bakshi in the study, "Intrinsic IL- 2 production by effector CD8 T cells affects IL-2 signaling and promotes
fate decisions, stemness, and protection," are Jennifer T. Ingram,
R. Curtis Hendrickson and Elliot J. Lefkowitz, UAB Department of
Microbiology; David K.

Crossman, UAB Department of Genetics; Laurie E. Harrington, UAB Department
of Cell, Developmental and Integrative Biology; and Casey T. Weaver,
UAB Department of Pathology. These UAB departments are all part of the
Marnix E.

Heersink School of Medicine.

Support came from National Institutes of Health grants AI049360,
AI156290 and TR003096; and the American Cancer Society award
PF-16-150-01-LIB. Zajac is a professor in the Department of Microbiology.

========================================================================== Story Source: Materials provided by
University_of_Alabama_at_Birmingham. Original written by Jeff
Hansen. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Shannon M. Kahan, Rakesh K. Bakshi, Jennifer T. Ingram, R. Curtis
Hendrickson, Elliot J. Lefkowitz, David K. Crossman, Laurie E.

Harrington, Casey T. Weaver, Allan J. Zajac. Intrinsic IL-2
production by effector CD8 T cells affects IL-2 signaling and
promotes fate decisions, stemness, and protection. Science
Immunology, 2022; 7 (68) DOI: 10.1126/ sciimmunol.abl6322 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220211161328.htm

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