**Core Concept**
Anti-HBs Ab refers to the presence of antibodies against the hepatitis B surface antigen. This immune response plays a crucial role in the diagnosis and management of hepatitis B infection. The presence of anti-HBs Ab indicates immunity to hepatitis B, either through vaccination or past infection.

**Why the Correct Answer is Right**
The presence of anti-HBs Ab signifies that the individual has developed an immune response against the hepatitis B virus (HBV). This occurs when the body produces antibodies against the HBsAg, the surface antigen of the virus. The anti-HBs Ab neutralizes the virus and prevents infection. The development of anti-HBs Ab is a critical indicator of immunity to HBV, which is essential for vaccine efficacy and disease prevention. The production of anti-HBs Ab is mediated by T-cell-dependent B-cell activation, involving the engagement of T-cells with antigen-presenting cells (APCs) and the subsequent activation of B-cells to produce antibodies.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because anti-HBs Ab does not indicate acute hepatitis B infection, which is characterized by the presence of HBsAg and IgM anti-HBc Ab.

**Option B:** This option is incorrect because anti-HBs Ab does not indicate chronic hepatitis B infection, which is characterized by the presence of HBsAg and anti-HBc Ab.

**Option C:** This option is incorrect because anti-HBs Ab does not indicate hepatitis B e-antigen (HBeAg) positivity, which is a marker of viral replication and infectiousness.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the presence of anti-HBs Ab in individuals who have not received the hepatitis B vaccine may indicate past infection and immunity to HBV. However, in vaccinated individuals, the presence of anti-HBs Ab confirms immunity, and a booster dose may not be necessary.

**Correct Answer: D. Immunity to hepatitis B.**