Figures & data
Figure 1. Three recognition strategies used by the innate immune defense. A: Recognition of microbial non-self induces immune response. B: Natural killer cells interact with target cells through activating and inhibitory receptors. When both types of receptors are engaged, the inhibitory receptors are dominant and the natural killer cell is not activated. However, if self marker molecules are missing, the natural killer cell is released from its state of inhibition. C: Expression of markers of altered self flags the cell for destruction.
Figure 2. Schematic and simplified overview of the development of the immune defense. Numbers of Toll-like receptors vary between species and tend to decrease during the course of evolution. Proteins belonging to the complement system are present in the purple sea urchin. The South African clawed frog possesses an adaptive immune defense based on B and T lymphocytes.
