Our bodies are amazing feats of nature
Pathways that we understand through science
Among the most complex though, I would wager
Immunity, autoimmunity, and balance.
First there is the issue of barriers,
Skin, and gut, and membranes
Primary defense against invaders
Seems ordinary, but really far from mundane.
What comes next is not pure serendipity
Not chance but an evolutionary gift
We kill germs with innate immunity
Imprecise but efficient and swift.
Phagocytes, a fitting name for greed
Neutrophils, macrophages, dendritic cells
Summoned to areas of injury, they proceed
To ingest and digest and clear dead cells.
Complement, a cascade of proteases
Opsonize invading pathogens
Activated by three different pathways
Membrane attack complex a terminal engine.
Simultaneously, adaptive immunity
In special regions, lymph nodes and Peyer’s patches
B cells develop some memory
Immunoglobulins churned out in batches.
Helper Ts aid antibody production
Cytotoxic Ts kill the bugs hiding within
Regulatory Ts promote self toleration
MHCs on cell surfaces weigh in.
Many elements require orchestration
Helped along by a bevy of proteins
Chemokines, interleukins, growth factors, interferons
Enzymatic cascades form routine.
This cellular/molecular adventure
Fantastically intricate choreography
Self or non-self, intruder, interloper
Defense against microbial tomfoolery.
Dr. Chan practices rheumatology is Pawtucket, R.I.