Stories about: immunity

Microptosis: Programmed death for microbes?

trypanosoma parasites immune defense apoptosis microptosis
Trypanosoma parasites in a blood smear. (CDC)

Of the various ways for a cell to die — necrosis, autophagy, etc. — apoptosis is probably the most orderly and contained. Also called programmed cell death (or, colloquially, “cellular suicide”), apoptosis is an effective way for diseased or damaged cells to remove themselves from a population before they can cause problems such as tumor formation.

“Apoptosis has special features,” says Judy Lieberman, MD, PhD, an investigator in Boston Children’s Hospital’s Program in Cellular and Molecular Medicine. “It’s not inflammatory, and it activates death pathways within the cell itself.”

Conventional wisdom holds that apoptosis is exclusive to multicellular organisms. Lieberman disagrees. She thinks that microbial cells — such as those of bacteria and parasites — can die in apoptotic fashion as well. In a recent Nature Medicine paper, she and her team make the case for the existence of what they’ve dubbed “microptosis.” And they think it could be harnessed to treat parasitic and other infections.

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Our T-cells have been hiding something: Another way to kill bacteria

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Listeria bacteria on a plate. The biology of HIV/AIDS suggests T-cells have a hitherto unrecognized way of killing pathogens like these.

The immune system, despite its immense complexity, really has only a few ways to kill bacteria:

  • Neutrophils and macrophages can capture and digest extracellular bacteria (ones that live free in tissues and the bloodstream).
  • Peptides (protein fragments) can punch holes in bacterial membranes or cross the membranes to disrupt bacterial processes.
  • T-cells can kill cells infected by intracellular bacteria (ones that take up residence within cells).

It’s this last mechanism that I want you to pay attention to. The conventional wisdom has long held that T-cells can only kill intracellular bacteria indirectly by eliminating the cells they’ve infected. But a paper by Judy Lieberman, MD, PhD, of Boston Children’s Hospital’s Program in Cellular and Molecular Medicine, reveals that T-cells have a hitherto unnoticed way of directly killing intracellular bacteria And she only found it because of HIV/AIDS.

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