Medical Health Encyclopedia

The Infection Fighters. The primary infection-fighting units are two types of white blood cells: lymphocytes and leukocytes.

Lymphocytes include two subtypes known as T cells and B cells. Both types of cells are designed to recognize foreign invaders (antigens) and to launch an offensive or defensive action against them:

• B cells produce antibodies, which are separate agents that can either ride along with a B cell or travel on their own to attack the antigen.
• T cells have special receptors attached to their surface that recognize the specific antigen.

Antigens are large molecules (usually proteins) on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, drugs, and foreign particles. The immune system recognizes antigens and produces antibodies that destroy substances containing antigens.

T cells are further categorized as killer T cells or helper T cells (TH cells).

• Killer T cells directly attack antigens that occur in any cells that contain a nucleus.
• Helper T cells also recognize antigens, but their role is two fold. They stimulate B cells and other white cells to attack the antigen. They also produce cytokines, powerful immune factors that have an important role in the inflammatory response and subsequent cell overgrowth, primarily in the skin.

Text Continues Below

---

Helper T Cells and Autoantibodies. The actions of the helper T cells are of special interest in scleroderma. For some unknown reason, the T cells become overactive in scleroderma and mistake the body's own collagen as an antigen and trigger a series of immune responses to destroy the false enemy:

• TH cells stimulate B cells to produce antibodies. In the case of scleroderma, however, they appear to direct the B cells to produce autoantibodies.
• Autoantibodies are primary factors in the autoimmune process. They are designed to target specific cells in the person's own body (self antigens). They also remain in circulation to continue the defense against them.
• A number of autoantibodies are associated with scleroderma that are also common in other autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus. They include rheumatoid factor, anti-single-stranded DNA, and antihistone antibodies. Some known as antinuclear antibodies (ANAs) attack RNA or DNA, the genetic material itself.
• Most patients with systemic scleroderma (but not localized scleroderma) have one or more of three other autoantibodies. They do not appear at the same time and seem to relate to different phases of the disease process. They are anti-RNA polymerase III, anti-topoisomerase I (also called anti-DNA topo I), and anti-centromere antibodies. For example, anti-DNA topo I is particularly associated with diffuse cutaneous scleroderma and lung complications. Anti-centromere antibodies, on the other hand, are associated with a less severe form of the disease.
• Patients with both systemic and localized scleroderma tend to have higher than normal levels of autoantibodies to fibrillin 1, which is a protein found in muscle and other connective tissue. This autoantibody in localized scleroderma is more prevalent in some groups (such as Japanese and Native American) than in others (Caucasians, for example). It is not found in other autoimmune diseases.