Example 1
A virus attaches only to cells with receptor R. Which cells are initially susceptible in this simplified model?
Cells displaying a compatible receptor R can bind the virus; attachment is a requirement in the stated model.
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Year 11 · SACE Stage 1
Host entry and antigen recognition
Identify the molecules and routes involved in host–pathogen recognition.
Method and worked examples
Pathogens can enter through wounds or respiratory, digestive and reproductive surfaces. Some use specific attachment molecules that bind compatible host-cell receptors. This helps determine which cells they can infect. Viruses enter susceptible cells and use cellular resources to reproduce; not every pathogen must live inside a host cell.
An antigen is a molecular feature recognised by immune receptors or antibodies. Antigens can be self or non-self; recognition involves molecular fit. Major histocompatibility complex, or MHC, molecules display peptide fragments at cell surfaces for T-cell recognition. MHC presentation is different from an antibody binding a free antigen. Recognition and appropriate immune signals together help coordinate a response rather than every contact producing the same outcome.
Example 1
Example 2
Identify the role of a cell-surface MHC molecule displaying a peptide.
It presents a peptide fragment for recognition by an appropriate T-cell receptor.
Watch out: Viruses depend on host cells, but many bacterial and other pathogens can grow outside host cells.