Table 2.

Comparison of changes in adaptive immunity during aging (immunosenescence) and the absence/reduction of type I IFN [2,131].

Cell Type	Aging	Absence/Reduction in Type I IFN
DCs	↓ DC maturation and priming of T cells ↑ PD-L1/2 on cDCs	↓ moDC maturation and IL-12 production ↓ cDC maturation and priming of T cells
T cells	↓ CD4+ and CD8+ T cell expansion/survival ↑ Rapid activation of CD8+ T cell, high proliferation, and function resultant rapid fatigue ↓ Sensitivity to IFN-I signaling ↓ CD4+ memory T cells ↓ Memory T cell contraction ↑ PD-1 expression ↑ Pro-inflammatory Th17 cells ↓ Anti-inflammatory Treg suppression Initial low Th1/Th2 ratio leads to high viral titers and rapid switch to high ratio which leads to cytokine storm	↓ CD8+ and CD4+ T cell expansion/survival ↓ CD8+ T cell maturation and activation ↓ CD8+ memory T cell formation ↓ CD8+ memory T cell cytotoxic function ↓ Memory T cell contraction ↑ PD-1 expression and exhaustion of CD8+ T cells
B cells	↓ Vaccine seroconversion ↓ B cell proliferation ↓ T-bet expression ↓ Isotype switching ↓ Affinity maturation ↓ Antibody affinity	↓ B cell proliferation ↓ Plasma cell differentiation and antibody secretion ↓ T-bet expression ↓ Isotype switching ↓ Production of IgG2a, IgG1, IgG2b, and IgG3 antibodies
T and B Memory cells	↑ Tissue-specific-antibody experienced memory cells ↓ Naïve lymphocyte	↓ IgG1+ and CD86+ memory B cells ↓ Transcription factor Bcl-6 within Tfh cells

↓: decrease; ↑: increase.