To produce high-affinity antibodies, B cells must undergo iterative cycles of targeted mutagenesis and affinity-based selection. These cycles take place in a structure known as the germinal center, which forms in secondary lymphoid organs upon exposure to antigenic stimuli. Here, we summarize our current understanding of the germinal center reaction.

BACKGROUND It has already been found that very small embyronic-like stem cells (VSELs) are present in adult human tissues and organs. The aim of this study was to find if there exists any similar population of cells in cell cultures of reproductive tissues and embryonic stem cells, and if these cells have any relation to pluripotency and germinal lineage. METHODS AND RESULTS Here we report th...

Background: Male factors, mainly spermatogenesis disorder, are responsible for 20-30% of infertility occurred in different societies. One of the known causes of spermatogenesis disorder is chemotherapy in patients with cancer. The side effect of chemotherapic agents may last from 10 years up to the end of the life. Since dividing cells are mainly affected by anticancer drugs, the aim of the pre...

CD4 T cell activation is positively (CD28) and negatively (CTLA-4) regulated by the costimulatory ligands CD80 and CD86. A central question is how the balance between these two opposing forces is controlled as T cells differentiate. We have previously shown that CD28 signaling is absolutely required to prime naive CD4 T cells to differentiate into effectors that provide help for germinal center...

B cells responding to T-dependent antigen either differentiate rapidly into extrafollicular plasma cells or enter germinal centers and undergo somatic hypermutation and affinity maturation. However, the physiological cues that direct B cell differentiation down one pathway versus the other are unknown. Here we show that the strength of the initial interaction between B cell receptor (BCR) and a...

Morphogenetic cell interactions during development were studied by combining cell ablation and cell lineage tracing techniques in embryos of the leech Helobdella triserialis. Ablation of an identified ectodermal teloblast, or teloblast precursor blastomere, on one side of an early embryo was often found to result in the later abnormal migration of the progeny cells of the corresponding contrala...

Background: Neem leaves (Azadirachta indica L.) have been used for many therapeutic purposes and medicinal applications. The extract of this plant has been used in both male and female genders as a traditional agent to prevent early pregnancy. In this study, the effect of this extract was investigated histologically and morphometrically on the germinal epithelia of the seminiferous tubules, epi...

Upon activation, B cells divide, form a germinal center, and express the activation induced deaminase (AID), an enzyme that triggers somatic hypermutation of the variable regions of immunoglobulin (Ig) loci. Recent evidence indicates that at least 25% of expressed genes in germinal center B cells are mutated or deaminated by AID. One of the most deaminated genes, c-Myc, frequently appears as a ...

Somatic hypermutation is the most critical mechanism underlying the diversification of Ig genes. Although mutation occurs specifically in B cells during the germinal center reaction, it remains a matter of debate whether the mutation machinery also targets non-Ig genes. We have studied mutations in the 58 noncoding region of the Bcl6 gene in different subtypes of lymphomas. We found frequent hy...