Differential co-expression hub scatter plot from a microarray study of high and low immune responders to influenza vaccine. The horizontal axis measures the magnitude of the sum of the negative interactions that each gene has with other genes, where a negative interaction increases the probability of being a low immune responder to the vaccine. The vertical axis measures the positive interactions of each gene. The diagonal line represents the null expectation of a gene having the same number of positive and negative interactions. The size of a plot point indicates the size of the main effect of the gene and the color indicates whether the gene has a positive or negative effect on immune response. The arrow highlights an important gene (PIK3CD) due to its having a strong negative hub effect (below the diagonal line) but very little main effect (small plot point radius).