Sequence relationship analysis of the human (h) and mouse (m) (a) chemokines and (b) chemokine receptors. Phylogenetic trees were constructed using amino acid sequences with Clustal X and PAUP* (the neighbor joining method) programs . In (a), the GRO and IP10 groups of CXC chemokines and the MCP and MIP groups of CC chemokines (see also Figure 3) are circled. Red letters indicate proteins that are found in only mouse or human but not the other. Blue letters indicate proteins for which the relationships are uncertain.