The purpose of the blocking step is to reduce non-specific background staining by saturating protein-binding sites on the tissue section and the glass slide. Tissue sections contain many charged and hydrophobic sites (e.g., on collagen, exposed proteins, or Fc receptors) that can bind antibodies indiscriminately through non-specific ionic or hydrophobic interactions. If these sites are not blocked, the primary or secondary antibodies may stick to them, creating a diffuse stain that obscures the specific signal. Blocking is achieved by incubating the section with a high concentration of irrelevant proteins, such as normal serum from the species in which the secondary antibody was raised, or a solution of bovine serum albumin (BSA). These proteins adsorb to the non-specific sites, effectively 'blocking' them. When the specific antibodies are added later, they are much less likely to bind to these occupied sites, resulting in a cleaner background and a higher signal-to-noise ratio for the true antigen-antibody binding.

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Zambia

• Naomi Miselo – 31 pts

• Visual Pathway Lesions
• Positive and Negative Symptoms
• Hallucinations and Delusions
• Antipsychotic Medications
• Emergency: Environmental Emergencies