Same Target, Different Coat
Asystole

I wore my favourite coat to the lymph-node dance,
Thought a little crowd would give a bug a chance.
A B cell took one look and called a friend—
That was the beginning of a difficult end.

A naive T cell needs the right introduction:
Peptide and M-H-C start recognition.
CD28 meets B7 for the cue,
Co-stimulation says there's work to do.
Cytokines help shape which path to take;
Interleukin two helps the clones awake.
Clonal expansion, the numbers climb—
A matching little army keeping time.

Same target, different coat,
Change the heavy-chain constant note.
IgM to IgG, IgA or IgE,
Different jobs for an antibody.
Class switching keeps the binding aim;
A different constant region joins the game.

The B-cell receptor catches native antigen,
Takes it inside and shows a piece again.
On class two, a helper sees the clue:
A follicular T cell joins the crew.
CD40 ligand meets CD40 there,
Cytokines carry the news they share.
A-I-D starts class-switch recombination,
Changing the constant-region specification.

Same target, different coat—
I recognise that binding note.

IgG can tag me for a hungry cell;
Across the placenta it travels as well.
Secretory IgA guards a mucosal shore,
IgE arms mast cells waiting by the door.
Allergy and parasites can bring that scene alive;
Different antibody classes help the host survive.
Plasma cells send antibodies on their way,
Memory B cells can return another day.

Somatic hypermutation changes the binding region;
Selection favours stronger binders in that legion.
Affinity maturation improves the fit,
Class switching changes the job that goes with it.
Two processes, two things to recall—
A-I-D contributes to them both.

Same target, different coat,
Change the heavy-chain constant note.
IgM to IgG, IgA or IgE,
Different jobs for an antibody.
Class switching keeps the binding aim;
A different constant region joins the game.

I wore my favourite coat to the lymph-node dance.
They changed their coats. I had a smaller chance.