CD4 and triple-A syndrome: Research showed that there was a significant difference in immune cell infiltration between normal vascular and AAA specimens, and high proportions of CD4+ T cells, resting natural killer cells, activated mast cells, and 12 other types of immune cells were found in normal vascular tissues, whereas high proportions of macrophages, resting mast cells, CD8+ T cells, and six other types of immune cells were found in AAA tissues (Nie et al., 2020).