Human Immunity and Blood

Recurrent foetal loss is a characteristic of antiphospholipid syndrome. In experimental situation, passive transfer of cardiolipin antibodies into mice also results in recurrent foetal loss.

Macrophages have an impressive range of functions but appear unable to prime naive lymphocytes. 

Thymus is a primary lymphoid organ.

The immunoglobulin, which is abundant in human colostrum is immunoglobulin-A.

The naming of antibody classes is based on the heavy chain naming: IgA- alpha heavy chain, IgD- delta heavy chain and so on.

The myeloid progenitor hematopoietic stem cells are: monocytes, WBC, RBC, platelets and mast cells.

BOF is present in birds near cloaca, and is the site of B-cell production and maturation. While in humans it is absent, its function is performed by bone marrow. Removal of BOF in birds will be fatal in case of infections while humans will not be affected. In due course of evolution, humans adapted to bone marrow instead of BOF, but both avian and human B cells are the same. Therefore, BOF in humans will also be a site of B-Cell development and thus, the human immune system will be enhanced. The answer 2 can also be considered to be correct, as the current research supports the 3 answer but books still believe in 2.

Cell surface receptors include G protein-coupled receptors, enzymatic receptors (like receptor tyrosine kinases), and ligand-gated ion channels. Transcription factors are intracellular nuclear proteins that bind DNA - not cell surface receptors.

Humoral immunity is mediated by B cells and their secreted antibodies. B cells differentiate into plasma cells that produce antibodies which circulate in body fluids (blood, lymph) - the 'humor'. T cells are responsible for cell-mediated immunity, not humoral immunity.

T cell receptors (TCRs) recognize antigen only when presented by MHC molecules on antigen-presenting cells. Unlike antibodies, TCRs cannot bind free antigen. Options A, C, D are incorrect: TCRs are membrane proteins (not defined by glycosylation), they don't bind cytokines directly, and complement binding is not their function.

One of the most remarkable aspects of the human immune system is its diversity, i.e. the ability to recognise a wide range of antigens and to mount a specific antibody response. This is called clonal selection.

The CD3 complex is a multi-subunit protein complex normally expressed on T cells as part of the T cell receptor (TCR) complex. It's involved in signal transduction when the TCR binds antigen. CD3 is not expressed on B cells, granulocytes, or NK cells - these have their own marker molecules.

Adaptive (acquired) immunity involves B cells, T cells, and antigen-presenting cells (APCs like dendritic cells, macrophages). B cells produce antibodies, T cells mediate cellular immunity and help B cells, and APCs process and present antigen to activate lymphocytes. All three cell types are essential components of the adaptive immune system.

The hypervariable regions in the variable domains of antibodies (produced by B cells) are directly responsible for antigen specificity. These complementarity-determining regions (CDRs) form the antigen-binding site. While T cell receptors and MHC molecules are involved in immune recognition, the antibody hypervariable regions are the primary source of specificity at the molecular level.