The x-axis is the 'Years since first infected with HIV' going from 0 to 10 in increment of 1. The y-axis is the 'Concentration of cells in blood per cubic millimeters'. The helper T cell concentration increases to nearly 800 in the first year and then gradually decreases to 0 through the years. The HIV concentration peaks to nearly 900 and decreases totally in the first years and then gradually increases to nearly 900 through the years.