Research up to now has tried but failed to decipher the cross-talk between 'killer T-cells' and' helper T-cells' in the fight against viruses.

Immunologists now recognize a four-point response system of helper t cells: Th 1, Th 2, Th 17 and regulatory t cells.

The host cells in question are immune-system cells called T-cells. Specifically, they are "helper" T-cells, which orchestrate the immune system's response to pathogens such as viruses.