1. Early nonspecific responses. Such as fever, ejection (vomiting, etc.) and phagocytosis. The latter (phagotytosis) is where the body envelopes the antigen — a white blood cell is a phagocyte that envelops (engulfs) bacteria. A big sign that nonspecific responses are going on is inflammation which is a process that indicates that signaling proteins such as interferons are identifying that a foreign body (antigen) has been identified and where it is located — bringing in nonspecific killer cells, such as white blood cells.
This phase takes place within hours of the antigen entering the body.
2. If the early nonspecific responses are insufficient at controlling/eliminating the antigen then what is called “cell mediated immune responses” kick in. Of these the most important are the so-called “T cells.” There are three types of T-cells: Helper, Signaling and Killer. The signaling cells tell the body’s immune system that an antigen is detected. The helper cells come along to try and identify the antigen specifically. The killer cells kill your cells that are infected by the antigen. Note that in the absence of helper cells, the killer cells are relatively indiscriminate — meaning they kill a lot of cells that are not infected with the problem antigen.
This phase takes place within days of the antigen entering the body.
3. The third phase is called the humoral immune response. This is where the body starts trying to build antibodies. Antibodies in the viral case are proteins that “kill” the antigen itself, while leaving the cells that are infected by the antigen alone. T-cells (above) kill your body’s cells as a way to stop the virus from replicating. Antibodies kill the virus itself (which also stops replication). It is antibodies that confer immunity to a given virus.
This phase also takes place within days of the antigen entering the body
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The problem is that the body is not that good at making antibodies. It can make antibodies but it is not certain that the antibodies will be effective against the antigen. This is the case for the herpes virus, for example. You get tested for HSV-1 (cold sores, one in two Americans are infected) and HSV-2 (genital herpes, one in four Americans are infected) by testing for antibodies to HSV-1 & HSV-2. So, yes, the body produces antibodies in response to a herpes infection. But those antibodies are obviously ineffective at killing the HSV-1 and HSV-2 viruses — if they were, people would “get over” a bout of herpes the same way they get over chicken pox.
In fact, one of the research paths in developing an effective vaccine for herpes is developing a better antibody than the body develops.
I just reposted guidance from WHO cautioning that there is not as of yet evidence that people exposed to SARS 2 (coronavirus) develop immunity. Thought it might help if I wrote out what they are saying in my own words. Mistakes here are my own. My understanding is that the body has ~four basic immune responses to antigens. Antigens are simply any foreign substance in the body that produces an immune response. Examples of antigens include viruses, bacteria, toxic chemicals, etc. Those immune responses are: 1. Ejection: i.e. throwing up, sneezing, coughing, diarrhea, etc. Something that throws whatever it is inside your body to the outside of your body. 2. Fever: elevating the body temperature to a level above which the antigen cannot remain viable. 3. Antibodies: Specific chemicals produced by the body that "kill" the antigen itself. This is the basis of vaccines. Antibodies have a degree of "memory" associated with them in that for some of the antigens can be used to provide immunity of various timelines. 4. T-cells. Specifically cytotoxic T-cells. These are chemicals produced by the body that kill cells in the body that are infected with the antigen, preventing the antigen from replicating. Note the difference in function between antibodies and T-cells. In the COVID-19 case, for example, antibodies would kill the SARS 2 virus itself. T-cells don't kill the virus but they do kill your cells that are infected by the virus. Both methods prevent reproduction by the virus but via different mechanisms. In general, antibody responses are specific to the antigen (a virus in this case). Antibodies are surgery with a Exacto-knife. T-cells are surgery with a flamethrower. Or think of antibodies as the "liberal" response of your immune system. Analytical and specific but requiring a lot of analysis and time and subject to indecision. Antibodies say "We need to understand this." T-cells are the "conservative" response of your immune system. Authoritarian and indiscriminate. Kill first, ask questions later. T-cells say "He who hesitates is lost." Both have their place. The WHO advice that I posted earlier this morning basically says: "We have not yet seen evidence that there is an effective antibody response to SARS 2, therefore antibody tests may provide a false sense of security that a person is 'immune' to SARS 2" Instead, WHO surmises, the dominant way that the body may deal with SARS 2 is via a T-cell response that effectively creates a "herd immunity" inside your body by just killing any of your cells that is infected. And if that is the case it means that someone could be infected over and over by SARS 2, hopefully having their T-cells beat the infection back each time. But they do not become immune. Now the two biggest problems with T-cell response are: 1. There is little of the "memory" function of antibodies. Cytokines (of "cytokine storm" fame) alert cytotoxic T cells to the presence of an infection but they don't really convey any information about the nature of infection. They just say "Something don't look right over here and you know how I love the smell of napalm in the morning." And then the T-cells nuke the whole planet, because that's the only way to be sure. Note that I said "little," not "none." There are certain T cells (called "memory T cells") that are responsible for saying "I've seen this before." Memory T cells help the cytotoxic T cells discriminate better. A memory T cell might tell the cytotoxic ones "Don't kill those cells over there, they just have common flu coronavirus. Or those over there, that's just herpes." But absent the memory T cells, the cytotoxic T cells just go after anything that looks different, kills them all and counts on God to sort it out. 2. Nukeing the whole planet nukes the whole planet. In this case the cure can become truly worse than the disease as the T-cells just kill a fatal number of your own cells. The immune system is one of many systems in the body that God obviously outsourced the design of to an intern.