Lymph node positioning for activation, differentiation, and elicitation. Numbered locator pins denote 1. CD4+ T cell activation (Baptista et al, 2019; Gerner et al, 2015; Gerner et al, 2017); 2. CD8+ T-cell activation (Bajenoff et al, 2003); 3. CD4+ T cell help for CD8+ T cells (Castellino et al, 2006); 4. Th1 differentiation (Groom et al, 2012); 5. Th2 differentiation (Leon et al, 2012); 6. Tfh differentiation (Kerfoot et al, 2011); 7. CD8+ Tcm activation (Kastenmuller et al, 2013); 8. Tfh help for B-cell maturation (Gitlin et al, 2014)