This activation is also aided by two other mechanisms. First, memory cells have increased numbers of adhesion molecules (LFA-1, CD2, LFA-3 and ICAM-1) on their surface as well as a higher population of affinity receptors.Thus, memory cells produce high concentrations of IL-2 to recruit more helper cells of both types TH1 and TH2. The recognition of antigen involves several receptors on the surface of the T cells. In contrast, B cells recognize antigen by surface-bound immunoglobulin and recognize the same epitopes somewhat differently. T cells only recognize haptens (small molecules) when the haptens are coupled to a carrier protein while antibody can recognize free haptens easily.
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