The primary immune response involves
a. a slow rise in the concentration of antibodies, followed by a gradual decline.
b. an immediate increase in the concentration of antibodies, followed by an immediate and sharp decline.
c. a slow rise in the concentration of antibodies, followed by a rapid decline.
d. an immediate increase in the concentration of antibodies, followed by a slow decline.

d. an immediate increase in the concentration of antibodies, followed by a slow decline.

Explanation:

The Primary Immune Response is mediated by antibodies, which are gamma globulin proteins formed by plasma cells (B lymphocytes). Plasmocyte is a differentiated B lymphocyte capable of actively secreting antibodies.

Antibodies are produced with the main function of neutralizing and eliminating an antigen that stimulated their production. This elimination process is done in various ways through complement fixation, opsionization, anaphylactic reaction (mast cell degranulation), substance neutralization, agglutination, etc.

To neutralize the antigen, the primary immune response promotes an immediate increase in antibody concentration. This is usually a quick process.  This concentration usually begins to decline in a slow process, but it will vary depending on the antigen.

endo:

regulates body hormones, aldosterone, vasopressin

neural:

signal, regulates body using electric signals, reflex

endo has to do with hormones; aldosterone and vasopressin are both hormones. i also had this question and got it right : d