In addition, helper T cell activation causes an upregulation of molecules expressed on the T cells surface, such as CD40 ligand (also called CD154), which provide extra stimulatory signals typically required to activate antibody-producing B cells. Gamma delta T cells
Gamma delta T cells (γδ T cells) possess an alternative T-cell receptor (TCR) as opposed to CD4+ and CD8+ (αβ) T cells and share the characteristics of helper T cells, cytotoxic T cells and NK cells. The conditions that produce responses from γδ T cells are not fully understood. Like other unconventional T cell subsets bearing invariant TCRs, such as CD1d-restricted natural killer T cells, γδ T cells straddle the border between innate and adaptive immunity. On one hand, γδ T cells are a component of adaptive immunity as they rearrange TCR genes to produce receptor diversity and can also develop a memory phenotype. On the other hand, the various subsets are also part of the innate immune system, as restricted TCR or NK receptors may be used as pattern recognition receptors. For example, large numbers of human Vγ9/Vδ2 T cells respond within hours to common molecules produced by microbes, and highly restricted Vδ1+ T cells in epithelia respond to stressed epithelial cells. Humoral immune response
A B cell identifies pathogens when antibodies on its surface bind to a specific foreign antigen. This antigen/antibody complex is taken up by the B cell and processed by proteolysis into peptides. The B cell then displays these antigenic peptides on its surface MHC class II molecules.
Arachnodactyly ("spider fingers") is a medical condition that is characterized by fingers and toes that are abnormally long and slender, in comparison to the palm of the hand and arch of the foot. In some cases, the thumbs of an individual with the condition are pulled inwards towards the palm. This condition is present at birth. Causes
This feature can occur on its own with no underlying health problems, or it can be associated with certain medical conditions, including Marfan syndrome, Ehlers–Danlos syndromes, Loeys–Dietz syndrome, and homocystinuria. It is also seen in congenital contractural arachnodactyly, which is caused by mutation in the gene encoding fibrillin-2 on chromosome 5q23. Notable cases
It remains unconfirmed whether composer Sergei Rachmaninoffs abnormally large reach on a piano was a result of arachnodactyly due to Marfan syndrome, as the pianist exhibited no other signs of the disease.It is also uncertain if blues guitarist and vocalist Robert Johnsons long fingers were attributed to the disease also due to Marfan syndrome. See also
Marfanoid

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