​In an experiment using nude mice, the population is divided into two groups, A and B.

• Group A mice are injected with T cells from normal mice.
• Group B mice are left untreated.
• Both groups are then immunized with LPS (Lipopolysaccharide).

Which one of the following statements regarding antibody production in groups A and B is most likely to be true?

Correct option is A

​Explanation:

1. Nude mice lack a thymus
• Nude mice (Foxn1^nu/nu) have a genetic mutation that causes thymic aplasia, meaning they lack mature T cells due to an absent thymus.
• This impairs their T-dependent immune responses (B cell activation requiring T-cell help).
2. LPS (Lipopolysaccharide) is a T-independent antigen
• Thymus-independent (TI) antigens can stimulate B cells without T-cell help.
• LPS is a TI-1 antigen (Thymus-Independent Type 1), meaning it can directly activate B cells, even in mice lacking T cells.
3. Effect of T-cell transfer on LPS response
• Group A (with T-cell injection): T cells are present but not required for an LPS response.
• Group B (without T-cell injection): B cells alone are sufficient to respond to LPS.
• Since LPS does not require T cells, both groups should show similar antibody responses.
4. Analysis of Answer Choices:
• (a) Correct → Both groups will produce similar antibody levels since LPS is a thymus-independent antigen.
• (b) Incorrect→ Even though these mice lack a thymus, thymus-independent responses still occur.
• (c) Incorrect→ TI antigens do not require T-cell activation (contradictory statement).
• (d) Incorrect→ The presence of T cells does not interfere with the production of antibodies against a T-independent antigen.

Information Booster:

1. Thymus-Independent Antigens (TI Antigens)
• TI-1 Antigens: Activate B cells via Toll-like receptors (TLRs), e.g., LPS (binds TLR4).
• TI-2 Antigens: Activate B cells via cross-linking of B-cell receptors (BCRs), e.g., polysaccharides from bacterial capsules.
2. Role of B Cells in T-Independent Responses
• Marginal zone B cells (MZ B cells) and B1 B cells respond well to TI antigens.
• Antibody response is mainly IgM, with minimal class switching (since T-cell help is required for switching to IgG, IgA).
3. T-Dependent vs. T-Independent Responses
• T-Dependent (TD) Antigens: Require T-cell help (e.g., proteins, vaccines).
• T-Independent (TI) Antigens: Do not require T cells (e.g., LPS, polysaccharides).