AP Syllabus focus:
‘Direct communication involves physical contact between cells, such as interactions of immune cells during antigen recognition and response.’
Direct contact signalling (juxtacrine communication) requires cells to touch, making it fast, spatially precise, and harder to “broadcast” than chemical signals. It is essential for immune recognition, development, and coordination between neighboring cells.
What “direct contact” communication means
Direct contact communication occurs when information passes between adjacent cells through membrane-bound molecules or intercellular connections. Because the signal is tied to contact, only cells that physically interact receive it, supporting specificity and local control.
Juxtacrine signalling: A form of cell communication that requires physical contact, in which a membrane-bound ligand or cell-surface marker on one cell binds a receptor on an adjacent cell.
Practice Questions
FAQ
MHC I typically presents peptides to cytotoxic T cells, whereas MHC II presents to helper T cells.
This biases the downstream response towards killing infected cells versus coordinating broader immune activity.
Activation usually requires additional membrane-bound “permission” signals beyond TCR–MHC binding.
Without these, the T cell may remain inactive or become tolerant.
Their channels have size and charge constraints, so small ions and small metabolites pass more readily than large proteins.
Channel opening can also be regulated by cellular conditions (e.g., ion concentrations).
It can be either.
One-way: a ligand-bearing cell triggers a response in a receptor-bearing neighbour.
Reciprocal: both cells receive signals due to paired receptor/ligand systems.
Direct connections reduce delays and prevent signal dilution.
This supports near-simultaneous changes in neighbouring cells, helping tissues behave as coordinated units rather than independent cells.
