| Criteria | Innate Immunity | Adaptive Immunity | Remarks |
| Definition | First line of defense with non-specific response | Second line of defense with antigen-specific response | Innate immunity is immediate and generalized; adaptive is specific and learned |
| Response Time | Rapid (within minutes to hours) | Delayed (days to weeks) | Adaptive immunity requires clonal expansion and differentiation |
| Specificity | Limited; recognizes PAMPs | High; recognizes specific antigens | Adaptive immunity provides tailored responses to individual pathogens |
| Immunological Memory | Absent | Present | Adaptive immunity becomes faster and stronger with repeated exposure |
| Receptors Used | Germline-encoded Pattern Recognition Receptors (PRRs) | Somatically recombined antigen-specific receptors (TCRs, BCRs) | PRRs are fixed and conserved; adaptive receptors are highly diverse |
| Major Cell Types | Macrophages, neutrophils, dendritic cells, NK cells | B cells, T helper cells, cytotoxic T cells, memory cells | Different cell populations mediate different phases of immune response |
| Diversity of Recognition | Limited (fixed number of PRRs) | High (due to receptor gene recombination) | Adaptive immunity can theoretically recognize millions of unique antigens |
| Effector Mechanisms | Phagocytosis, inflammation, complement activation, cytokine release | Antibody production, cytotoxic killing, cytokine signaling | Innate mechanisms clear most infections early; adaptive mechanisms finish the job |
| Duration of Response | Short-lived | Long-lasting | Adaptive response can persist for years via memory cells |
| Evolutionary Origin | Ancient; found in all multicellular organisms | Evolved in vertebrates only | Adaptive immunity evolved later as an advanced layer of defense |
| Activation Requirement | Constitutively active or activated by conserved molecules | Requires antigen presentation and costimulatory signals | Adaptive activation depends on the innate immune system’s initial response |
| Role in Vaccination | Minimal (acts as an adjuvant trigger) | Central role (generation of memory and antibodies) | Effective vaccines aim to stimulate adaptive immunity, often with innate system activation |
| Clinical Relevance | Early control of pathogens; inflammation; immune surveillance | Pathogen clearance; immune memory; autoimmunity; allergy | Both systems must function cooperatively for immune balance and effective defense |
