FRIDAY, April 11 (HealthDay News) -- Immune system T-cells don't
begin to multiply until up to three days after infection, an
unexpected finding that changes current thinking about how the
immune system responds to infection.
Researchers at the Scripps Research Institute in La Jolla,
Calif., said this delay in T-cell proliferation may be an
evolutionary safeguard against the risk of an autoimmune response
caused by a sudden increase in T-cells.
It had been believed that memory T-cells (which recognize
pathogens from previous infections) began to multiply much sooner
than naive T-cells.
"It was thought that memory T-cells responded more effectively
to infection by starting cell division earlier than naive cells and
by multiplying more rapidly after that," Lindsay Whitton, a
professor in the neuropharmacology department, said in a prepared
statement. "Our study shows that neither assumption is true. Even
though memory cells detected and responded to virus infection
within a few hours, they did not begin to divide until after a
lengthy delay. After that, cell division was rapid for both naive
and memory cells."
Once proliferation of both types of cells started, there was a
greater accumulation of memory T-cells, possibly because there were
already more of them prior to infection, Whitton said.
The findings were published in April 10 online issue of the
Public Library of Science Pathogens.
In this study, the Scripps team used laboratory animals to trace
the proliferation of CD4 and CD8 memory T-cells. CD4 cells help
regulate the immune system's response to pathogens such as bacteria
and viruses, while CD8 cells attack infected cells and may be play
a role in transplant rejection.
"The principal conclusions from our study are that, in a
virus-infected animal, both naive and memory CD4 T-cells shows a
similar and extended delay of approximately 72 hours before they
begin to divide, and that this is true in both lymphoid and
non-lymphoid tissues. This delay occurred despite the fact that the
viral antigen reached T-cell-stimulatory levels within six to 12
hours after infection," Whitton said.
She and her colleagues "were very much surprised by the
discovery that memory cells didn't begin proliferation sooner than
their naive counterparts. Memory T-cells are central to the
protective immunity of infections and vaccinations, because they
act against subsequent encounters with specific microorganisms.
Compared to naive cells, memory T-cells can be triggered by lower
antigen levels, and their initial response to infection, such as
the production of cytokines, is more rapid and more effective."
More information
The Nemours Foundation has more about the
immune system.
