Tuesday, January 6, 2015

Rhinovirus Replicates Best in the Nasal Cavity

It's that time of year, eh?  Cold and flu season.  And this week we have news from researchers giving us a bit more insight into the rhinoviruses that cause the common cold.

The unsurprising new discovery is that rhinoviruses replicate more efficiently—and therefore cause colds more effectively—in the nasal cavity than in the lungs because of a temperature difference.  In mice, the animals used in the recent study, the immune mechanisms that fight off rhinoviruses work better in the warmer environment of the lung than in the cooler environment of the nasal cavity.

This phenomenon may be why a cold generally doesn't wreak the same havoc in lungs as do other respiratory viruses like influenza viruses.  Rhinoviruses, as their name implies, generally remain limited to the nose.

What can we use from this in teaching undergraduate A&P?

  • When discussing the nasal cavity's vascularity and air-warming functions, we may want to point out that understanding the temperature gradient between the nose and lower respiratory tract has practical clinical applications.  Such as why some pathogens are limited to the nose. And why cold weather may contribute to rhinvirus infection.

  • When discussing immunology, we may want to mention that body temperature—and sometimes organ temperature—can have an impact on how efficiently our immune mechanisms fight infection.

  • One could consider steering a conversation about "there is still no cure for the common cold" to a conversation about the fact that scientists are still working on understanding rhinoviruses—"and, oh, did you hear the latest .....?"

Want to know more?

Where Rhinovirus Replicates Best
  • Tracy Vence,  The Scientist.  Online. January 6, 2015.
  • Plain-English summary of the discovery.
  • my-ap.us/1FgWKr7

Temperature-dependent innate defense against the common cold virus limits viral replication at warm temperature in mouse airway cells
  • Ellen F. Foxman, et al.  Proceedings of the National Academy of Science. Online. January 5, 2015. doi: 10.1073/pnas.1411030112 
  • Original research paper.
  • my-ap.us/1xA4v6m
Photo credit: mcfarlandmo

Friday, January 2, 2015

Fat Cells in Skin Kill Bacteria

Scientists reported today that adipocytes in mouse and human skin produce an antimicrobial peptide (AMP) called cathelicidin is response to Staph aureus infections, including MRSA. Experimental animals that were deficient in the AMP were more susceptible to skin infections.

Adipocytes may recognize S. aureus by detecting bacterial peptides with toll-like receptors (TLRs), but more work is needed to fully understand the mechanisms.

This finding adds more to our understanding of human skin as a vital part of our body's defenses against infection. It also opens the door to understanding how diabetes, metabolic syndrome, and other conditions can reduce resistance to skin infections by altering the availability of AMPs in the fat associated with skin.

All of this may eventually lead to additional—perhaps more effective—strategies in preventing or curing serious skin infections such as MRSA.

I realize that we generally think of fat cells as belonging to the hypodermis, not the dermis, as described in the research. However, recent evidence shows the presence of adipocytes in the dermis that are distinct from those in the hypodermis. These adipocytes derive from a common precursor cell that produces both dermal fibroblasts and intradermal adipocytes. These dermal adipocytes have been shown to have a role in wound healing and the regeneration of hair follicles. And the research summarized here suggests that they also have a role in immunity.

What can we use from this in teaching undergraduate A&P?

  • Mention this discovery when discussing the roles of adipose tissue and adipocytes in your coverage of tissues of the body.

    • Consider clarifying that dermal adipocytes are distinct from fat cells in the hypdermis. And perhaps mention that it's a detail often left out of introductory discussions of skin.

  • This is a good point to mention when discussing the protective functions of the skin when covering the integumentary system.

  • When discussing the immune system, this concept helps illustrate several important principles:

    • The role of the skin as the first line of defense against infection

      • The variety of mechanisms available in the skin to act defensively

    • The role of TLRs and pattern recognition in immunity

    • The fact that immunity is a role for many tissues—not just lymphocytes and other WBCs

  • Take a moment NOW to add this to your course notes!

Want to know more?

Killer Fat
  • J. Alcorn and J. Kolls. Science 2 January 2015: Science Vol. 347 no. 6217 pp. 26-27 DOI: 10.1126/science.aaa4567
  • Editorial summary of the research in plain English. Includes a really nice, simple illustration of the concept (includes FREE teaching slide)
  • my-ap.us/1vBWbNP

Dermal adipocytes protect against invasive Staphylococcus aureus skin infection
  • L. Zhang1, et al. Science 2 January 2015: Vol. 347 no. 6217 pp. 67-71 DOI: 10.1126/science.126097
  • Original research article. Additional images available here, including some nice micrographs showing increase in adipocytes in response to S. aureus infection
  • my-ap.us/1xePNS4

Defining dermal adipose tissue.
  • Driskell RR, et al. Exp Dermatol. 2014. Exp Dermatol. 2014 Sep;23(9):629-31. doi: 10.1111/exd.12450.
  • Review article describing dermal adipocytes.
  • my-ap.us/1GuH3bL

FREE teaching slide
Click the image
to download a

Adipose image credit: my-ap.us/13MYGWO
This post was updated 6 OCT 2015