7.0 - B Cells
B Cell Biology and Humoral Immunit
y
Primary and Secondary Humoral Immune Re
sponses
Primary Immune Response: Naive B cells encounter antigen, becom
e activated, and differentiate into antibody-secreting plasma cells. T
hese plasma cells produce antibodies specific to the eliciting antige
n.
Secondary Immune Response: The same antigen stimulates memor
y B cells, leading to a more robust and rapid production of specific a
ntibodies compared to the primary response. This is due to the pre-e
xisting memory B cells that have already encountered the antigen.
B Cell Development
B Cell Receptors (BCRs): Naive mature B cells express membrane-b
ound monomeric forms of IgD and IgM. These BCRs have two identic
al heavy chains and two identical light chains connected by disulfide
bonds, forming a basic "Y" shape.
BCR Structure: The constant region of the two heavy chains spans th
e B cell membrane, while the two antigen-binding sites are exposed
to the exterior of the B cell. These sites are responsible for binding sp
ecific pathogen epitopes, initiating the activation process.
BCR Abundance: Each naive mature B cell has upwards of 100,000 B
CRs on its membrane, all with identical epitope-binding specificity.
Classes of Immunoglobulins
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, Antigen Recognition and Antigen-Induced B
Cell Activation
Antigen Delivery: Antigens can be delivered to naive B cells in lymph
oid organs through various routes:
Small Antigens: Delivered through afferent lymphatics and conduit
s in follicles.
Large Antigens: Delivered by subcapsular sinus macrophages or d
endritic cells in the medulla.
Antigen Presentation: The antigen presented to B cells is generally i
n its intact, native conformation and is not processed by antigen-pre
senting cells.
Antigen Capture and Delivery to B Cells
BCR Complex: The BCR complex of mature B cells is composed of m
embrane Ig molecules that bind antigens and associated Igα and Ig
β proteins that deliver signals for B cell activation.
CR2 Coreceptor: B cell activation is facilitated by the CR2 coreceptor
on B cells, which recognizes complement fragments attached to the
antigen or part of immune complexes containing the antigen.
Toll-Like Receptors (TLRs): Microbial products engage TLRs on B cell
https://www.studyfetch.com/platform/studyset/6748730d72bff04b73915866/material/67864c7a773a477021358de3/document 23/1/25, 17:03
Page 2 of 9
B Cell Biology and Humoral Immunit
y
Primary and Secondary Humoral Immune Re
sponses
Primary Immune Response: Naive B cells encounter antigen, becom
e activated, and differentiate into antibody-secreting plasma cells. T
hese plasma cells produce antibodies specific to the eliciting antige
n.
Secondary Immune Response: The same antigen stimulates memor
y B cells, leading to a more robust and rapid production of specific a
ntibodies compared to the primary response. This is due to the pre-e
xisting memory B cells that have already encountered the antigen.
B Cell Development
B Cell Receptors (BCRs): Naive mature B cells express membrane-b
ound monomeric forms of IgD and IgM. These BCRs have two identic
al heavy chains and two identical light chains connected by disulfide
bonds, forming a basic "Y" shape.
BCR Structure: The constant region of the two heavy chains spans th
e B cell membrane, while the two antigen-binding sites are exposed
to the exterior of the B cell. These sites are responsible for binding sp
ecific pathogen epitopes, initiating the activation process.
BCR Abundance: Each naive mature B cell has upwards of 100,000 B
CRs on its membrane, all with identical epitope-binding specificity.
Classes of Immunoglobulins
https://www.studyfetch.com/platform/studyset/6748730d72bff04b73915866/material/67864c7a773a477021358de3/document 23/1/25, 17:03
Page 1 of 9
, Antigen Recognition and Antigen-Induced B
Cell Activation
Antigen Delivery: Antigens can be delivered to naive B cells in lymph
oid organs through various routes:
Small Antigens: Delivered through afferent lymphatics and conduit
s in follicles.
Large Antigens: Delivered by subcapsular sinus macrophages or d
endritic cells in the medulla.
Antigen Presentation: The antigen presented to B cells is generally i
n its intact, native conformation and is not processed by antigen-pre
senting cells.
Antigen Capture and Delivery to B Cells
BCR Complex: The BCR complex of mature B cells is composed of m
embrane Ig molecules that bind antigens and associated Igα and Ig
β proteins that deliver signals for B cell activation.
CR2 Coreceptor: B cell activation is facilitated by the CR2 coreceptor
on B cells, which recognizes complement fragments attached to the
antigen or part of immune complexes containing the antigen.
Toll-Like Receptors (TLRs): Microbial products engage TLRs on B cell
https://www.studyfetch.com/platform/studyset/6748730d72bff04b73915866/material/67864c7a773a477021358de3/document 23/1/25, 17:03
Page 2 of 9
