B lymphocytes are the mediators of humoral immunity; constitutes 10–15% of blood lymphocytes. They are named after their site of maturation (bursa of Fabricius in birds and bone marrow in humans and other mammals). B cells proliferate through various stages, first in bone marrow, then in peripheral lymphoid organs (Fig. 1)

Fig1. B cell development.

Development of B Cells in Bone Marrow

 Initial stages of B cell proliferation occur in bone marrow; independent of exposure to antigen.

- Pro-B Cells (Progenitor B Cells): They are the earliest bone marrow cells of B cell lineage. They do not produce immunoglobulins (Ig) but express a heterodimer Igα/Igβ that forms a part of the B cell receptor (BCR) in future

- Pre-B Cells (Precursor B Cells): Pro-B cells differentiate into pre-B cells by expressing μ heavy chain

- Immature B Cells: Pre-B cells proliferate into immature B cells by expressing light chain

* B cell receptor: Heavy chain μ and its light chain join to form complete IgM molecule. IgM is then complexed with heterodimer Igα/Igβ on the B cell surface to form B cell receptor (Fig. 2)

* Tolerance: Some of the immature B cells are capable of reacting to self-antigens. Tolerance to those B cells are essential for prevention of autoimmunity. Following contact with a self-antigen, the tolerance is developed either by:

^ Receptor editing: A process by which the Ig genes coding light chains are rearranged so that a different (edited) B cell receptor is produced which no longer reacts to self-antigen or

^ Negative selection: By apoptosis of self-reacting immature B cells in spleen.

Fig2. Structure of B cell receptor (BCR) and pre-BCR.

Development of B Cells in Peripheral Lymphoid Organs

Immature B cells migrate from bone marrow to peripheral lymphoid organs (lymph node and spleen) where they transform into mature B cells following contact with appropriate antigen.

Mature or Naive B Cells

 Most mature B cells (95%) belong to the follicular B cell type and produce surface receptor IgD in addition to IgM.

They play an important role in humoral immune response

- Following antigenic stimulus, the mature B cells transform into activated B cells (lymphoblasts) which further differentiate into either effector B cells, i.e. plasma cells (majority) or memory B cells

- Plasma cells (antibody secreting cells): They are oval, large (15 µm size), with an eccentrically oval nucleus containing large blocks of peripheral chromatin (cartwheel appearance) and the cytoplasm containing abundant organelles. They have a short life span of two or three days.

However, there are few rare mature B cell types such as B-1 cell and marginal zone B cells which have limited diversity and are components of innate immunity.

- B-1 cells: They are found mostly in the peritoneal cavity, coated by surface markers IgM (natural antibodies) and CD5 molecules, but lack IgD

- Marginal-zone B cells: They are present at the edges of lymphoid follicles of spleen and are produced in response to the polysaccharide antigens.

B cells are the main components of humoral immunity; produce five classes of antibodies, which in turn have various biological functions

Differences between T cell and B cell are given in Table 1.

Table1. Differences between t cell and B cell.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الصيانة يواصل أعمال البنى التحتية في مشروع استراحة الواحة على طريق (النجف - كربلاء)

جامعة الكفيل تختتم دورة تدريبية مخصصة لتنمية المهارات وتعزيز الانضباط الوظيفي

المجمع العلمي يجري اختباره للمتقدمين على قناة حفظة القرآن الكريم في النجف الأشرف

قسم الشؤون الدينية ينظّم الدورة التأهيلية الثانية للمتقدّمين للتعيين في العتبة العباسية المقدسة

المزيد

الآخبار الصحية

هل يمكن الاعتماد على "ChatGPT" في الحصول على نصائح صحية؟

قبل أي نشاط رياضي.. هذه الفاكهة ينصح بها الخبراء

استخدام القنب للعلاج.. دراسة تحذر من من "جنون العظمة" ؟!

غالبية الناس ينظفون أسنانهم خطأ.. إليك الطريقة الصحيحة

المزيد

الآخبار التكنلوجية

نصائح لإطالة عمر بطارية السيارة وضمان أدائها الأمثل

الرياض تحتضن مونديال الرياضات الإلكترونية بدعم stc

"ستارشيب" ينطلق في رحلة تجريبية ويسقط بالمحيط الهندي !

شركة جديدة.. خطة ماسك لمنافسة مايكروسوفت في الذكاء الاصطناعي

المزيد

مواضيع ذات صلة

Macrophage

T Lymphocytes

Immunologic Manifestations of Infectious Mononucleosis

Peripheral Lymphoid Organs

Central Lymphoid Organs

Effector Functions of Complement

Complement Pathways

Mechanisms of innate immunity

Immunologic Manifestations of Viral, Rickettsial, and Mycoplasmal Diseases

Immunologic Manifestations of Fungal Diseases

The Structure of Antibodies

Myelomas and Monoclonal Antibodies