Main Difference – Primary vs Secondary Immune Response
Humoral immunity is a component of adaptive immunity, which generates specific immune responses to a particular foreign material. The immune response generated by humoral immunity can be categorized into two as primary immune response and secondary immune response. The main difference between primary and secondary immune response is that primary immune response occurs in response to the primary contact with the antigen whereas secondary immune response occurs in response to the second and subsequent exposure to the same antigen.
Key Areas Covered
1. What is Primary Immune Response
– Definition, Facts, Antibodies
2. What is Secondary Immune Response
– Definition, Facts, Antibodies
3. What are the Similarities Between Primary and Secondary Immune Response
– Outline of Common Features
4. What is the Difference Between Primary and Secondary Immune Response
– Comparison of Key Differences
Key Terms: Antibodies, Antibody Titer, Humoral Immunity, IgG, IgM, Primary Immune Response, Secondary Immune Response
What is Primary Immune Response
Primary immune response refers to any immune response of the immune system that includes the production of antibodies and/or cell-mediated immunity. It occurs following the first exposure to a foreign antigen. At the beginning of the primary immune response, there are no previously produced antibodies. Hence, naive B cells are activated and differentiated into antibody-producing plasma B cells. Some of the B cells develop into memory cells. The lag phase, i.e., the time period in which antibodies are produced against a particular antigen, of the primary immune response is long. Sometimes the lag phase can be as long as weeks or months. The generation of primary and secondary immune responses over time is shown in figure 1.
Figure 1: Primary and Secondary Immune Response
The amount of the antibodies produced or the antibody titer is low in the primary immune response. IgM is the main type of antibodies produced in the primary immune response. Over time, the antibody titer becomes undetectable.
What is Secondary Immune Response
Secondary immune response refers to any immune response of the immune system that occurs in response to the subsequent exposure to a particular antigen. The second exposure may occur even after a year. Due to the presence of memory cells, the lag phase of the secondary immune response is shorter than that of the primary immune response. IgG is the main type of antibodies produced and small amounts of IgM, IgA, and IgE are also produced. A high antibody titer is produced during the secondary immune response. The production of antibodies from the memory cells in the secondary immune response is shown in figure 2.
Figure 2: Antibody Production from Memory B cells
The antibodies produced by the secondary immune response remain in the body for a longer period of time.
Similarities Between Primary and Secondary Immune Response
- Primary and secondary immune responses are two types of immune responses generated by the humoral immunity.
- Antibodies are produced in both primary and secondary immune responses.
Difference Between Primary and Secondary Immune Response
Definition
Primary Immune Response: Primary immune response refers to any immune response of the immune system that includes the production of antibodies and/or cell-mediated immunity.
Secondary Immune Response: Secondary immune response refers to any immune response of the immune system that occurs in response to the subsequent exposure to a particular antigen.
Occurrence
Primary Immune Response: Primary immune response occurs in response to the primary contact of the antigen.
Secondary Immune Response: Secondary immune response occurs in response to the second and subsequent exposure to the same antigen.
Responding Cells
Primary Immune Response: Naive B cells and T cells respond to the antigens during the primary immune response.
Secondary Immune Response: Memory B cells respond to the antigens during the secondary immune response.
Lag Phase
Primary Immune Response: The lag phase of the primary immune response is long (4-7 days).
Secondary Immune Response: The lag phase of the secondary immune response is short (1-4 days).
Antibody Peak
Primary Immune Response: The antibody level reaches its peak in 7-10 days.
Secondary Immune Response: The antibody level reaches its peak in 3-5 days.
Time Taken to Establish Immunity
Primary Immune Response: Primary immune response takes a longer time to establish the immune response.
Secondary Immune Response: Secondary immune response takes short time to establish the immune response.
Types of Antibodies
Primary Immune Response: A large amount of IgM and a small amount of IgG are produced during the primary immune response.
Secondary Immune Response: A large amount of IgG, a small amount of IgM, IgA, and IgE are produced during the secondary immune response.
Amount of Antibody
Primary Immune Response: Generally, only a few antibodies are produced in primary immune response.
Secondary Immune Response: 100-1000 times more antibodies are produced in secondary immune response.
Remaining Antibodies
Primary Immune Response: The antibody level declines rapidly in primary immune response.
Secondary Immune Response: The antibody level remains for a long time in secondary immune response.
Affinity of Antibody
Primary Immune Response: Antibodies show low affinity to their antigens in primary immune response.
Secondary Immune Response: Antibodies show high affinity to their antigens in secondary immune response.
Appearance
Primary Immune Response: Primary immune response appears mainly in the lymph nodes and spleen.
Secondary Immune Response: Secondary immune response appears mainly in the bone marrow and then, in the spleen and lymph nodes.
Thymus-dependent/Thymus-independent Antibodies
Primary Immune Response: Both thymus-dependent and thymus-independent antibodies are involved in the primary immune response.
Secondary Immune Response: Only thymus-dependent antibodies are involved in the secondary immune response.
Conclusion
Primary and secondary immune responses are two types of immune responses that mediate humoral immunity. Primary immune response occurs with the first contact of the antigen. It mainly produces IgM antibodies. Secondary immune response occurs with the second or subsequent exposure to the same antigen. It mainly produces IgG antibodies. This the difference between primary and secondary immune response.
Reference:
1. Ademokun, Alexander A, and Dunn‐Walters, Deborah “Immune Responses: Primary and Secondary.” Encyclopedia of Life Sciences, Available here.
Image Courtesy:
1. “2223 Primary and Secondary Antibody Respons new” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “2222 Clonal Selection of B Cells” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
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