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Humoral Immune Responses

Humoral Immune Responses

T Cell Activation and Clonal Selection

T Cell Activation and Clonal Selection

T cells are integral to our adaptive immune system, recognizing and effectively responding to foreign antigens. T cell activation and clonal selection are pivotal in orchestrating this immune response. This article elucidates these mechanisms, detailing the roles of cluster of differentiation (CD) markers, major histocompatibility complex (MHC) molecules, costimulatory signals, and the process of clonal selection.
Naive T cells that have not yet encountered an antigen express two primary CD...

Antigens Involved in Adaptive Immunity

Antigens Involved in Adaptive Immunity

An antigen is any substance the immune system identifies as foreign and potentially harmful to the body, prompting an immune response. Antigens have two functional properties: immunogenicity and reactivity. Immunogenicity is the ability of an antigen to stimulate a specific immune response. At the same time, reactivity describes the antigen's ability to react with the cells and antibodies produced in response to it.
Complete Antigens
Complete antigens possess both immunogenicity and reactivity.

B Cell Activation and Differentiation

B Cell Activation and Differentiation

The adaptive immune response, a sophisticated defense mechanism, relies on the activation and differentiation of B lymphocytes, or B cells. These processes enable our bodies to mount a tailored response against specific pathogens such as bacteria, free virus particles, toxins, and parasites.
When naive B cells encounter a specific antigen that can bind to the B cell receptor (BCR) on their surface, they undergo sensitization to respond to the antigen's presence. Sensitization begins with...

Diversity of Antigen Receptors

Diversity of Antigen Receptors

Antigen receptors are essential components of the immune system crucial in defending the body against foreign invaders. These receptors are present on the surface of B and T cells, enabling them to recognize antigens and mount an appropriate immune response.
Before encountering any antigen, lymphocytes express these receptors. On B cells, the antigen receptor is a membrane-bound antibody molecule called BCR; on T cells, it is a T cell receptor or TCR. B and T cell receptors are composed of two...

Complement System

Complement System

The complement system is a group of approximately 20 plasma proteins that strengthen the body's defenses against infections through opsonization, inflammation, and cell lysis. Opsonization involves coating pathogens with complement proteins, making them more recognizable and facilitating phagocyte engulfment. Certain complement proteins induce inflammation that attracts immune cells to the site of infection. Cell lysis involves the destruction of pathogens through the formation of a membrane...

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Measuring Erythrocyte Complement Receptor 1 Using Flow Cytometry

Measuring Erythrocyte Complement Receptor 1 Using Flow Cytometry

Published on: May 19, 2020

Complement receptors CD21 and CD35 in humoral immunity.

Ramon Roozendaal¹, Michael C Carroll

¹Immune Disease Institute, Harvard Medical School, Boston, MA 02115, USA.

Immunological Reviews

|September 14, 2007

Summary

Follicular dendritic cells (FDCs) use complement receptors CD21 and CD35 to capture immune complexes, which is crucial for memory B-cell survival. Antigen transport to FDCs occurs rapidly in lymph, dependent on the complement system.

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Murine Model of CD40-activation of B cells

Murine Model of CD40-activation of B cells

Published on: March 5, 2010

Area of Science:

Immunology
Complement System Biology

Background:

The complement system is vital for innate and adaptive immunity.
Complement receptors CD21 and CD35 recognize activated complement products and are found on B cells and FDCs.
FDC-expressed CD21 and CD35 are key for immune complex uptake and retention.

Purpose of the Study:

To review the role of FDC-expressed CD21 and CD35 in humoral immunity.
To investigate the mechanism of antigen transport to FDCs.

Main Methods:

Review of existing literature on complement receptors and humoral immunity.
Multiphoton intravital imaging to observe antigen transport in vivo.

Main Results:

FDC-expressed CD21 and CD35 are essential for memory B-cell survival.
Absence of these receptors impairs memory B-cell survival, potentially due to lack of antigen or C3d.
Small protein antigens rapidly enter B-cell follicles via lymph.
Antigen uptake by FDCs is complement-dependent.

Conclusions:

FDC complement receptors play a critical role in maintaining humoral immunity and memory B-cell populations.
Complement-dependent antigen uptake by FDCs is a rapid process occurring in lymph follicles.